Sometimes your computer may actually turn on but an error message during the Power On Self Test (POST) will stop the boot process. Other times your PC may simply freeze during the POST with no error at all.
There are a number of BIOS error messages that can display on your monitor and several reasons why a PC might freeze during the POST so it's important that you step through a logical process like the one I've created below.
Important: If your PC is in fact booting through the POST, or is not reaching the POST at all, see my How to Fix a Computer That Won't Turn On guide for more applicable troubleshooting information.
Time Required: Anywhere from minutes to hours depending on why the computer stopped booting during the POST
Troubleshoot the cause of the BIOS error message you see on the monitor. These errors during the POST are usually very specific so if you've been fortunate enough to receive one, your best course of action is to troubleshoot to the specific error you see.
If you don't fix the problem by working through the specific error during the POST, you can always return here and continue with the troubleshooting below.
Disconnect any USB storage devices and remove any discs in any optical drives. If your computer is trying to boot from a location that doesn't actually have bootable data on it, your computer could freeze somewhere during the POST.
Note: If this works, be sure to change the boot order, making sure that your preferred boot device, probably the internal hard drive, is listed before USB or other sources.
Clear the CMOS. Clearing the BIOS memory on your motherboard will reset the BIOS settings to their factory default levels. A misconfigured BIOS is a common cause of a computer locking up during the POST.
Important: If clearing the CMOS does fix your problem, make any future settings changes in BIOS one at a time so if the problem returns, you'll know which change caused your issue.
Test your power supply. Just because your computer initially turns on does not mean that the power supply is working. The power supply is the cause of startup problems more than any other piece of hardware in a computer. It very well could be the cause of your problems during the POST.
Replace your power supply immediately if your tests show a problem with it.
Important: Do not skip a test of your PSU thinking that your problem can't be with the power supply because your computer is receiving power. Power supplies can, and often do, partially work and one that isn't fully functional must be replaced.
Try reseating the following and then see if your computer boots past the POST:
Note: Unplug and reattach your keyboard and mouse as well. There's little chance that the keyboard or mouse is causing your computer to freeze during the POST but just to be thorough, we should reconnect them while we're reseating other hardware.
Reseat the CPU only if you think that it may have come loose or might not have been properly installed.
Note: I separated out this task only because the chance of a CPU coming loose is slim and because reseating one could actually create a problem if you're not careful. There's no reason to worry as long as you appreciate how sensitive a CPU and its socket/slot on the motherboard is.
Triple check every hardware configuration if you're troubleshooting this problem after a new computer build or after installation of new hardware. Check every jumper and DIP switch, verify that the CPU, memory, and video card you're using is compatible with your motherboard, etc. Rebuild your PC from scratch if necessary.
Important: Do not assume that your motherboard supports certain hardware. Check your motherboard's manual to verify that the hardware you've purchased will work properly.
Note: If you haven't built your own PC or haven't made hardware changes then you can skip this step entirely.
Check for causes of electrical shorts inside your computer. This could be the cause of the problem if your computer freezes during the POST, especially if it does so without a BIOS error message.
Start your PC with essential hardware only. The purpose here is to remove as much hardware as possible while still maintaining your computer's ability to power on.
- If your computer starts normally with only essential hardware installed, proceed to Step 9.
- If your computer still isn't displaying anything on your monitor, proceed to Step 10.
Important: Starting your PC with its minimum necessary hardware is very easy to do, takes no special tools, and could provide you with valuable information. This isn't a step to skip if, after all the steps above, your computer is still freezing during the POST.
Reinstall each piece of hardware that you removed in Step 8, one piece at a time, testing your PC after each installation.
Since your computer powered on with only the essential hardware installed, those parts must working properly. This means that one of the hardware components you removed is causing your computer to not turn on properly. By installing each device back into your computer and testing each time, you'll eventually find the hardware that caused your problem.
Replace the nonfunctioning hardware once you've identified it. See these Hardware Installation Videos for help reinstalling your hardware.
Test your computer's hardware using a Power On Self Test card. If your computer is still freezing during the POST with nothing but essential computer hardware installed, a POST card will help identify which piece of remaining hardware is causing your computer to stop booting.
If you don't already own or are unwilling to buy a POST card, skip to Step 11.
Replace each piece of essential hardware in your PC with an identical or equivalent spare piece of hardware (that you know is working), one component at a time, to determine which piece is causing your computer to stop during the POST. Test after each hardware replacement to determine which component is faulty.
Note: The average computer owner doesn't have a set of working spare computer parts at home or work. If you don't either, my advice is to revisit Step 10. A POST card is very inexpensive and is, in general and in my opinion, a smarter approach than stocking spare computer parts.
Finally, if all else fails, you'll probably need to find professional help from a computer repair service or from your computer manufacturer's technical support.
If you don't have a POST card or spare parts to swap in and out, you're left not knowing which piece of your essential computer hardware is not working. In these cases, you'll have to rely on the help of individuals or companies that do have these tools and resources.
Note: See the first tip below for information on getting more help.
Is your computer still not booting past the Power On Self Test? See Get More Help for information about contacting me on social networks or via email, posting on tech support forums, and more. Be sure to tell us what you've already done to try to fix the problem.
Did I miss a troubleshooting step that helped you (or might help someone else) fix a computer that's freezing or showing an error during the POST? Let me know and I'd be happy to include the information here.