Start with the simplest fixes first

Most computer problems go away after a restart. Power off completely, wait 30 seconds, and turn it back on. If the machine won't start at all, check that the power cable is plugged in at both ends — into the wall outlet and into the back of the computer. Look for a light on the power supply or motherboard; if there's no light, the power connection is broken.

If the computer starts but nothing appears on the screen, try these steps in order: unplug the monitor cable from the back of the computer and plug it back in firmly; if the monitor has its own power button, make sure it's on; try a different power outlet for the monitor; restart the computer while the monitor is plugged in and powered on.

For a computer that runs slowly or freezes, restart first. Then check how much space is left on the hard drive by opening File Explorer (Windows) or Finder (Mac), right-clicking the drive, and selecting Properties or Get Info. If the drive is more than 90 percent full, the computer will slow down noticeably. Delete large files you no longer need, or move them to an external drive.

Key Takeaways

  • Restart the computer completely before trying anything else — this fixes most temporary problems like freezing or slow performance.
  • Check physical connections: power cables, monitor cables, and keyboard or mouse connections are often loose and cause the computer to appear broken.
  • A hard drive that is more than 90 percent full will make the computer run slowly, and deleting old files or moving them to external storage fixes this.
  • If the computer will not start and you see no lights or sounds, the power supply may have failed and the computer may need professional repair or replacement.
  • Malware and viruses slow down computers and cause crashes; running a full scan with your antivirus software can find and remove these threats.

Check for malware and viruses

Malware and viruses are programs that run without your permission and slow down the computer, cause crashes, or steal information. If your computer is running slowly or showing pop-up windows you did not click on, malware is likely the cause.

Windows computers come with Windows Defender, which is built into the operating system. Open Windows Security by typing "Windows Security" in the search box at the bottom left of the screen. Click "Virus & threat protection," then "Scan options," and select "Full scan." This scan takes 30 minutes to several hours depending on how much data is on the drive. Let it finish without interrupting.

Mac computers come with XProtect, which runs automatically in the background. You can also read Malwarebytes for Mac from the Malwarebytes website, install it, and run a full scan. Restart the computer after the scan finishes.

Update the operating system and drivers

The operating system is the software that runs the computer — Windows or macOS. Updates patch security holes and fix bugs that cause crashes. Check for updates by going to Settings on Windows or System Preferences on Mac.

On Windows 10 or 11, open Settings, click "Update & Security" or "System," then "Windows Update," and click "Check for updates." If updates are available, click "Install now" and restart the computer when prompted. Do not turn off the computer during an update.

On Mac, open System Preferences, click "Software Update," and install any updates shown. Restart when prompted.

Drivers are software that let the computer talk to hardware like printers, graphics cards, and network adapters. Outdated drivers cause crashes and slow performance. On Windows, open Device Manager by right-clicking the Start button and selecting Device Manager. Look for any devices with a yellow warning triangle. Right-click the device and select "Update driver," then choose "Search automatically for updated driver software." Restart the computer when finished.

Clear temporary files and cache

Temporary files and cache are data the computer stores to speed up common tasks, but they pile up over time and waste space. Clearing them often fixes slow performance.

On Windows, open Settings, click "System," then "Storage," and click "Temporary files." Check the boxes next to "Temporary files," "Recycle Bin," and "Temporary internet files," then click "Remove files." This takes a few minutes.

On Mac, open Finder, click "Go" at the top, hold down the Option key, and click "Library." Open the "Caches" folder. Select all files by pressing Command+A, then drag them to the Trash. Empty the Trash by right-clicking it and selecting "Empty Trash."

Check for hardware problems

If the computer still does not work after trying the steps above, a hardware part may have failed. The most common failures are the hard drive, power supply, and RAM (memory).

Listen to the computer when it starts. A clicking or beeping sound usually means the hard drive is failing. A computer that turns on but when ready turns off usually has a power supply problem. A computer that starts but crashes randomly or shows a blue screen with an error message often has failing RAM.

You can run a hard drive test on Windows by opening Settings, clicking "System," then "Storage," and looking for "Disk usage." If the disk shows red or is completely full, the drive may be failing. On Mac, restart the computer and hold Command+D to run the Apple Diagnostics test. This test checks RAM, the hard drive, and other hardware and takes a few minutes.

If a hardware test shows a problem, the part will need to be replaced. This usually requires taking the computer to a repair shop or sending it to the manufacturer.

Reinstall the operating system as a last resort

If nothing else works, reinstalling Windows or macOS can fix deep software problems. This erases everything on the computer, so back up all your files first to an external drive or cloud storage.

On Windows 10 or 11, open Settings, click "System," then "Recovery," and click "Reset this PC." Choose "Remove everything" and follow the steps. The computer will restart several times and take 30 minutes to an hour.

On Mac, restart the computer and hold Command+R to enter Recovery Mode. Click "Reinstall macOS" and follow the steps. This also takes about an hour.

After reinstalling, the computer will be like new. You will need to sign back into your accounts and reinstall your programs.

When to take the computer to a repair shop

Take the computer to a repair shop if it makes unusual noises like clicking or grinding, if it overheats and shuts down on its own, if the screen is cracked or flickering, or if it does not turn on at all after you have checked the power cable.

Also take it in if you see a blue screen with an error message that appears repeatedly, if the keyboard or trackpad does not respond, or if you spilled liquid on it. Liquid damage can cause short circuits that are dangerous to repair yourself.

Before you go, write down exactly what the computer does — does it not start, does it crash after five minutes, does it make a noise — and when it started happening. This information helps the repair shop diagnose the problem faster.

Frequently Asked Questions

What should I do if my computer is making a loud beeping noise?

Beeping usually means the RAM is not seated properly or has failed. Try turning off the computer, unplugging it, waiting 30 seconds, and opening the case if you are comfortable doing so. Look for RAM sticks (long rectangular chips) and push them down firmly into their slots. Close the case and restart. If beeping continues, the RAM may have failed and needs replacement.

Why does my computer run slowly even after I restart it?

Check the hard drive space first — if it is more than 90 percent full, delete old files. Then run a full malware scan with Windows Defender or Malwarebytes. Open Task Manager on Windows (Ctrl+Shift+Esc) or Activity Monitor on Mac (Command+Space, type "Activity Monitor") and look for programs using a lot of CPU or memory. Close programs you are not using. If it is still slow, update the operating system and drivers.

Can I fix a computer that will not turn on?

First check that the power cable is plugged in at both the wall and the computer. Look for a light on the power supply. If there is no light, try a different outlet. If there is still no light, the power supply has likely failed and needs to be replaced by a repair shop. If there is a light but the computer does not start, the motherboard or CPU may have failed.

Is it safe to open my computer case?

Yes, if you ground yourself first to avoid damaging parts with static electricity. Touch a metal part of the case before touching any components inside. Wear an anti-static wrist strap if you have one. Take a photo of the inside before you remove anything so you remember how to put it back. If you are not comfortable opening the case, take the computer to a repair shop instead.

What is the difference between restarting and shutting down?

Restarting turns the computer off and back on when ready, which clears memory and reloads the operating system. Shutting down turns the computer off completely. Restarting is better for fixing temporary problems because it clears more data from memory. Shut down only when you are done using the computer for the day.