By Austin Little
A computer that was fine yesterday and crawls today usually has a reason you can find. Here is how to track it down, fix it yourself, and know when it's time for help.
AI disclosure. This page was drafted with AI assistance and edited for Apiary. We don't invent quotes, stats, people, or events. If something looks off, tell Austin — that's the point of a living hive.
It was fine yesterday. Today the mouse stutters, the browser takes forever to open, the fan sounds like a hair dryer, and every click comes with a spinning wheel. You didn't drop it. You didn't install anything weird. At least, you don't think you did.
Here's the encouraging part: when a computer slows down suddenly, there is almost always a specific cause, and most of the causes are things a regular person can find and fix in an afternoon. Slow-and-getting-slower-over-years is a different story (we'll cover that too). But sudden slowness is like a car that suddenly pulls to one side. Something changed. Your job is to find out what.
This guide is written for the person who just wants their computer back. No jargon without an explanation. Steps for both Windows and Mac. And clear signs for when to stop and get a pro, because a few causes of slowness are actually warnings that you're about to lose your files.
First: back up anything you can't lose
Before you troubleshoot, do one thing: if there are photos, documents, or files you would cry about losing, copy them somewhere else now. A USB drive, an external hard drive, or a cloud service you already use.
Why first? Because one cause of sudden slowness is a failing storage drive, and a failing drive can go from "slow" to "won't start" without much warning. If your computer is slow because the drive is dying, every hour you spend troubleshooting is an hour of extra wear. Back up, then investigate.
If the computer is so slow that copying files is painful, prioritize: the irreplaceable stuff first (family photos, your only copy of something), the replaceable stuff later.
The 60-second fixes (try these before anything else)
These solve a surprising number of "it's suddenly slow" cases. Try them in order.
1. Actually restart it
Not sleep. Not closing the lid. A real restart.
On Windows: Start menu → Power → Restart. )
On a Mac: Apple menu → Restart.
A restart clears out programs that have gotten stuck, memory that never got released, and background tasks that went haywire. Lots of people haven't truly restarted their computer in weeks. If that's you, this might be the whole fix.
2. Close the browser tabs
Modern web browsers treat many tabs like separate little programs, and some websites — especially ones with video, ads, or live-updating feeds — keep using your computer's power even when you're not looking at them. Thirty open tabs can eat a lot of memory.
Close what you don't need. If you're a tab hoarder (no judgment), bookmark the important ones into a folder and close the rest. Most browsers also have a built-in task manager or performance page that shows which tabs are hogging resources.
3. Check whether an update is running
This is one of the most common causes of "suddenly slow." Windows and macOS both download and install updates in the background. While that's happening, the computer can be sluggish for a while, sometimes an hour or more on older machines. Antivirus programs, cloud storage apps, and big programs like Office also update themselves.
- Windows: Settings → Windows Update. If it says it's downloading or installing, let it finish, then restart.
- Mac: Apple menu → System Settings → General → Software Update.
If an update just finished, the first restart afterward often clears up the slowness. If the slowness started right after an update and doesn't go away after a couple of restarts, keep reading — we'll cover that.
4. Plug it in (laptops)
Many laptops automatically slow themselves down on battery to save power, and some slow way down when the battery is nearly empty or the battery is worn out. If your laptop is unplugged, plug it in and see whether things perk up. Also check your power mode: on Windows, it's under Settings → System → Power & battery. On a Mac, Low Power Mode lives in the Battery settings.
5. Look at the cloud sync icon
OneDrive, iCloud, Google Drive, and Dropbox all sync files in the background. If you just added a lot of photos, or the service decided to re-check everything, it can chew through your computer's power and internet connection for hours. Look for the cloud icon near the clock (Windows) or in the menu bar (Mac). If it says it's syncing a mountain of files, that's likely your culprit. You can pause it temporarily.
Find the culprit: open the "what's using my computer" screen
If the quick fixes didn't help, it's time to look under the hood. Both Windows and Mac have a built-in tool that shows exactly which programs are using your computer's resources right now. This is the single most useful troubleshooting step in this whole article.
On Windows: Task Manager
Press Ctrl + Shift + Esc. (Or right-click the Start button and choose Task Manager.) If you see a tiny window, click "More details."
Go to the Processes tab. You'll see columns for:
- CPU — the computer's brain. How hard it's thinking.
- Memory — the short-term workspace (also called RAM).
- Disk — how busy your storage drive is.
- Network — how much internet it's using.
Click a column header to sort by it. Now look for anything sitting near the top using a lot.
On a Mac: Activity Monitor
Press Command + Space, type "Activity Monitor," and press Return. You'll see tabs across the top: CPU, Memory, Energy, Disk, Network. Click the "% CPU" column to sort. On the Memory tab, look at "Memory Pressure" at the bottom — a green graph is fine; yellow or red means the computer is running short on memory.
How to read what you see
A few plain-English rules:
- One program near 100% CPU for a long time is suspicious. Sometimes it's a program that's stuck. Sometimes it's a legitimate task (a video export, a virus scan). If you don't recognize it, search the exact name online before you do anything.
- Memory almost full means the computer is juggling too many things and has started using the storage drive as overflow, which is much slower. Close programs, close tabs, or consider a memory upgrade later.
- Disk at or near 100% constantly on Windows is a classic cause of a computer that feels frozen. It might be an update, an antivirus scan, a search index rebuilding, cloud sync, or — on older machines with spinning hard drives — a drive that's struggling.
- Network busy when you're not doing anything might be an update, cloud sync, or something you didn't sign up for.
Ending a stuck program
If you find a program you recognize that's clearly stuck (for example, a browser using an enormous amount of memory), you can close it:
- Windows: Select it in Task Manager → End task.
- Mac: Select it in Activity Monitor → click the X button at the top → Quit (or Force Quit if it won't respond).
A warning: don't end processes you don't recognize just because they have scary names. Many system processes are supposed to be there, and ending them can freeze the computer or cause it to restart. Look it up first.
The common causes, one by one
Here are the usual suspects behind a sudden slowdown, roughly from most common to least common, with what to do about each.
Too many programs starting when you turn it on
Every program that launches at startup sits in the background using memory and processing power. Installers love to add themselves to this list without asking clearly. One new app might not matter. Ten of them add up.
Windows: Open Task Manager → Startup apps (or the Startup tab). You'll see a list with an "impact" rating. Right-click anything you don't need running all the time — game launchers, chat apps you rarely use, updaters for programs you barely open — and choose Disable. Disabling doesn't uninstall; it just stops the program from launching automatically.
Mac: Apple menu → System Settings → General → Login Items. Remove things you don't need at login with the minus button. There's also a section listing apps allowed to run in the background; you can switch off ones you don't recognize as needed (look them up first).
Restart and see whether things are snappier.
Your storage drive is nearly full
When the storage drive gets close to full, computers slow down. The operating system needs free space for temporary files, updates, and memory overflow. When there's no room, everything gets cramped.
Check how full it is:
- Windows: Settings → System → Storage.
- Mac: Apple menu → System Settings → General → Storage.
Free up space:
- Empty the Recycle Bin or Trash. (Seriously, people forget this one.)
- Clear out the Downloads folder. It's often full of installers and files you used once.
- Uninstall programs you don't use. On Windows: Settings → Apps → Installed apps. On a Mac: drag apps from the Applications folder to the Trash, or use the Storage settings.
- Move big photo and video collections to an external drive (after confirming they're backed up).
- On Windows, turn on Storage Sense, which can automatically clean up temporary files.
- On a Mac, the Storage settings page offers recommendations like emptying Trash automatically and optimizing storage.
Watch out for one trap: cloud storage apps that are set to keep every file downloaded on your computer. Many let you switch to "files on demand" so only the files you open take up space.
An update went sideways
Sometimes an update finishes, the computer restarts, and it's slower than before. A few possible reasons:
- The system is still doing post-update housekeeping, like rebuilding its search index. Give it a day of normal use with the computer plugged in and awake.
- A driver (the small piece of software that talks to your hardware, like the graphics chip) didn't update cleanly.
- A specific update has a bug affecting certain machines. When this happens to many people at once, it usually shows up in tech news within days.
What to try:
- Restart twice. Really.
- Check for more updates. Often a fix follows a buggy update.
- On Windows, check for driver updates through Windows Update's optional updates section or your computer maker's support site.
- On Windows, as a last resort, you can uninstall a recent update under Settings → Windows Update → Update history → Uninstall updates.
Malware or unwanted software
Malicious software — viruses, crypto-mining programs, adware, browser hijackers — can slow a computer dramatically. Warning signs:
- New toolbars, a changed homepage, or a search engine you didn't pick.
- Pop-ups even when your browser is closed.
- Programs you don't remember installing.
- The fan running hard and CPU usage high even when you're doing nothing.
- Friends say they got weird messages from your email or social accounts.
What to do:
- Windows: Run a full scan with Windows Security (the built-in antivirus, sometimes called Microsoft Defender). Search "Windows Security" in the Start menu → Virus & threat protection → Scan options → Full scan. Microsoft also offers an "offline scan" option that restarts the computer to catch tougher infections.
- Mac: macOS has built-in malware protections that update in the background. If you suspect adware, check your Applications folder and browser extensions for anything you don't recognize, and remove it. A reputable, well-known security app can do a second-opinion scan.
- Everyone: Check your browser extensions (the little add-ons). Remove any you don't recognize or don't use. Extensions are a common way unwanted software sneaks in.
Avoid "free PC cleaner" pop-ups that claim your computer has 3,000 problems. Many of these are scareware — the thing they're warning you about is themselves.
Too little memory for what you're asking it to do
Memory (RAM) is your computer's countertop. Storage is the pantry. When the countertop is full, the computer keeps walking back and forth to the pantry, and everything slows down. Modern websites and apps use more memory than they used to, so a computer that was fine a few years ago can feel cramped today, and it can feel suddenly cramped when you start using a new heavy app or a new website your work requires.
If Task Manager or Activity Monitor regularly shows memory nearly maxed out, you have three options: use fewer programs at once, upgrade the memory (on computers that allow it — many newer laptops and all recent Macs have memory soldered in and can't be upgraded), or eventually replace the computer.
Overheating
Computers protect themselves from heat by slowing down. This is called thermal throttling, and it's designed to prevent damage. Signs: the fan is loud, the bottom of the laptop is hot, and the computer gets slower the longer you use it.
What to do:
- Don't use a laptop on a bed, couch cushion, or blanket, which block the vents.
- Use it on a hard, flat surface.
- Look at the vents. If they're clogged with dust (common in homes with pets), gentle blasts of compressed air can help. Power the computer off and unplug it first. Hold fans still while you blow, since spinning them with air can damage them.
- Desktop towers collect dust inside. If you're comfortable, you can open the side panel (unplugged) and dust it out. If not, a computer shop can do it.
A failing storage drive (this one is serious)
Older computers often use a spinning hard drive (HDD). Newer ones mostly use solid-state drives (SSDs), which are faster and have no moving parts. Both can fail.
Warning signs of a failing drive:
- Clicking, grinding, or buzzing sounds from inside the computer (spinning drives).
- Files that won't open or come up corrupted.
- Extremely slow performance with the disk at 100%, even after restarts.
- Freezing when opening files or folders.
- Error messages about the disk, or the computer failing to start.
What to do: Stop troubleshooting and back up your important files now. Then get the drive checked. On Windows, many drive makers offer free tools that read the drive's built-in health report (called SMART data). On a Mac, Disk Utility has a "First Aid" feature that can check for problems. But if you hear clicking, don't run lots of tests — every minute of use can make things worse. Get the data off first, and if the files are precious and the drive won't cooperate, talk to a professional data recovery service before trying anything else.
Your antivirus is fighting itself
If you have two antivirus programs installed — say, one that came preinstalled as a trial and Windows' built-in protection, or two third-party products — they can conflict and slow everything down. Pick one. Windows Security is built in on Windows. If you choose a third-party product, make sure only one real-time scanner is active.
It's your internet, not your computer
Sometimes "my computer is slow" is really "my internet is slow." If only websites and streaming are slow, but opening files and programs feels normal, test your internet speed on a speed-test website, restart your router and modem (unplug for about 30 seconds, plug back in), and see whether other devices in the house are also slow.
If the computer has been slowly getting worse for years
Sudden slowness has a trigger. Gradual slowness is usually a pile of small things: more startup programs, fuller drives, heavier websites, and software updates designed with newer hardware in mind.
A few things genuinely help older computers:
- Upgrade from a spinning hard drive to an SSD. On computers that allow it, this is often the single biggest speed boost an older machine can get. A shop can do it and copy your files over.
- Add memory, if your computer allows it.
- A clean reinstall of the operating system. Both Windows and macOS have built-in options to reset or reinstall. This wipes out years of clutter but takes time, and you must back up first. On Windows, see Settings → System → Recovery. Apple publishes official instructions for reinstalling macOS.
Things that generally don't help, despite the ads:
- "Registry cleaners" and "PC optimizer" programs. At best they do little; at worst they cause problems.
- "RAM booster" apps.
- Defragmenting an SSD. Windows handles SSD maintenance on its own, and manually defragmenting an SSD isn't recommended. (Defragmenting an old spinning hard drive can help a bit, and Windows usually does that on a schedule too.)
Call a pro when...
You can handle a lot of this yourself. But get help from a reputable repair shop, your computer maker's support, or your workplace IT team when:
- You hear clicking or grinding, or see disk errors. Back up first, then get help.
- You suspect ransomware — files renamed with strange extensions, a message demanding payment. Disconnect from the internet and get professional help. Don't pay first and ask later.
- It's a work computer. Your IT team may have rules, monitoring, or software you shouldn't remove.
- It won't boot, or it restarts by itself in a loop.
- It smells like burning, the battery is swelling (the case bulges, the trackpad lifts), or it gets too hot to touch. A swollen lithium-ion battery is a fire hazard. Stop using and charging it, and get it to a professional.
- You'd need to open a laptop to clean or upgrade it and you're not comfortable. Laptops have tiny ribbon cables that tear easily.
And a scam warning: real tech support companies do not call you out of the blue, and real Microsoft or Apple warnings don't come as browser pop-ups with phone numbers. If a pop-up tells you to call a number because your computer is infected, close the browser. Never give a stranger remote access to your computer because they called you.
A printable fix list
Work down this list until things get better:
- Back up irreplaceable files.
- Restart (real restart).
- Close extra browser tabs and programs.
- Let updates finish; restart again.
- Plug in the laptop; check power mode.
- Check cloud sync; pause if it's churning.
- Open Task Manager / Activity Monitor; find what's hogging CPU, memory, or disk.
- Disable unnecessary startup apps.
- Free up storage space.
- Run a full malware scan; remove unknown browser extensions.
- Check for heat and dust.
- Watch for drive-failure signs; get help if you see them.
- Test your internet if only the web is slow.
Frequently asked questions
Why is my computer slow right after an update?
Often it's still finishing background work like indexing files, optimizing apps, or installing a follow-up piece. Restart a couple of times and give it some normal use while plugged in. If it's still slow after a day or two, check for further updates and driver updates.
Is 100% disk usage bad?
Occasionally hitting 100% is normal during updates or scans. Staying at 100% for long periods, with everything frozen, is a problem worth tracking down. Common causes include updates, search indexing, cloud sync, antivirus scans, low memory, and on older machines, a struggling hard drive.
Will deleting files make my computer faster?
If your drive is nearly full, yes, freeing space can make a real difference. If you already have plenty of free space, deleting more won't do much.
Do I need to buy antivirus software?
Windows comes with built-in protection (Windows Security), and macOS has built-in protections as well. Many people do fine with those plus careful habits. What matters most is having one active protection tool, keeping your system updated, and not installing software from sketchy sources.
How do I know if it's time for a new computer?
If you've done the cleanup, it's running a supported operating system, and it's still too slow for what you need — or it can no longer get security updates — it may be time. Before you replace it, ask a shop whether an SSD or memory upgrade is possible. That can stretch an older machine's life.
Can my phone slow down my computer?
Not usually by itself. But phone backup and photo-sync apps on your computer can run heavy background tasks after you connect your phone or take a lot of photos.
The takeaway
When a computer gets slow all of a sudden, something changed. Back up your important stuff first. Then work from simple to serious: restart, close tabs, let updates finish, look at what's hogging your computer in Task Manager or Activity Monitor, trim startup apps, free up space, scan for malware, and check for heat. Most of the time, one of those is the answer.
And listen for the warning signs that this isn't a cleanup job: clicking sounds, disk errors, a bulging battery, or ransom notes. Those are the moments to stop fiddling and call a pro. Your files matter more than your pride.