• PC World
• »Computers
• »Desktops

Problem: Your computer won't boot.

The Fix: You'll have to play Sherlock Holmes to figure out what's dead. Take it step-by-step.

1. First thing: Check all cables (including the plug into the electric socket) to make sure everything is hooked up nice and tight.
2. Next, see if the power supply turns on. Listen for the sound of its fan or of your hard drive spinning. If you hear nothing, your power supply probably needs to be replaced. To confirm, consider testing the voltage output with a power-supply tester such as PC Power and Cooling's $10 ATX). Of course, you should also check your home's circuit breaker before doing major PC surgery, and try powering another device from that outlet to make sure it's getting juice.
3. If your power supply is okay but nothing appears on screen, plug in a different monitor (borrow one if you must) to ensure it's not your display that's blown. If the monitor proves to be good, try replacing the video cable. Still nothing on screen? If your drive is spinning normally, your video card is probably bad. To replace it, see our video guide, "How to Replace a Graphics Board," or use the video output integrated into your PC's motherboard, if it has that feature. While your case is open, make sure all the fans inside work when you power on the PC. You could have excess-heat issues.
4. If your monitor is working but you detect no hard-drive activity and see no display (or you see a display but the PC can't get through boot-up), reset the CMOS. Shut down the PC, unplug it, ground yourself, and take out the battery on the motherboard (click on photo above). Wait 5 minutes, and consult your PC manual or go to the vendor's Web site for instructions on resetting the CMOS jumpers. Reboot and see if that fixed the problem.
5. If the PC is still not functioning, bad RAM could be the culprit. Remove one memory module at a time (or replace each module with a known good one) and reboot after each test. Alternatively, create a free MemTest86 boot disk on another PC, and try using it to test the RAM.
6. If none of this works, your motherboard or CPU is probably damaged, and will need to be replaced (cost: $80 to $300 or more). However, your data is probably still intact and can be recovered if you install your hard drive on another system. Consider going to a repair shop for an estimate on the repair; it may be more cost-effective to replace the PC. Also, a repair shop might be your best (and only) option if your PC is a laptop.
7. Finally, if the PC's BIOS routine runs but the drive won't spin, your drive may have crashed. See "Problem: Your hard drive has crashed" for help with that.

What If It's the OS?

As dire as these hardware failures seem, you're far more likely to encounter software issues, such as Windows refusing to start or freezing while it's loading. Here's how to get back up and running if your operating system is the problem.

1. Boot into Safe Mode. As Windows starts up, press the key as directed to reach the boot menu. Select Safe Mode. Often, Windows will recover if you boot into Safe Mode and then shut down and reboot normally. With Windows Vista, you can also try the 'Repair Your Computer' option by selecting it at the boot menu (if you don't have that option, check your Vista DVD for it). You'll have various choices to aid your PC: 'Startup Repair' is worth a shot.
2. No results? Try 'Last Known Good Configuration' at the boot menu, which is especially helpful if you have recently changed hardware or drivers. If this works, remove new hardware (which may be incompatible) and roll back drivers in Device Manager. Right-click My Computer (Computer in Vista), click Hardware (in XP), and choose Device Manager.
3. If you can run Safe Mode but not regular Windows, try System Restore (via Programs, Accessories, System Tools in XP; in Vista, click Start, type system, and choose System Restore from the Programs list) to roll back your PC to when it did work. The PC might have become unstable after an automatic download and installation of an update or other unattended download (you may want to change any default settings that allow such unattended installs to happen). Run antivirus and antispyware apps in Safe Mode, too.
4. If you still can't boot, you probably have heavy-duty Windows problems. Try to boot from an emergency CD like a Knoppix disc or an Active Boot Disk, which can help you to see whether your PC will boot at all and to collect any critical files from the drive.
5. If your PC is still unstable, reinstalling Windows is probably your best bet. You can do this chore while leaving data intact by using a standard Windows installation CD. In rare cases, vendor-provided recovery disks will perform non-data-destructive OS reinstalls too; check your manual to see if yours can. See our directions on reinstalling XP and on reinstalling Vista.

How to Avoid It Next Time: PCs typically die unexpectedly, so focus on getting up and running quickly: Turn on System Restore, keep your system-recovery discs and copies of critical apps handy for reinstalls, back up often, and keep a spare hard drive and power supply. Using a drive-image program such as the $50 Acronis True Image 10 or the $70 Norton Ghost 10 can make it much easier to restore your PC and data, too. If you can, have a second PC to use in emergencies if your main system needs repair.