For the past 5 hours my self built desktop has crashed at startup, just after reaching the Windows XP loading screen (it never makes it to login). It has a Pentium 4 3.2Ghz Processor, 1024Mbs of memory, and all its fans are working. I suspect it's some kind of power supply problem because the desktop takes longer to restart each time it crashes. Also, whenever I bypass Windows startup and go to my BIOS control screen, the computer crashes as soon as I've exited that screen.

You will have to list the configuration.
BIOS version, mobo EXACT brand/model/version, memory (brand/model) CPU (CPU-ID if possible) psu (W) VGA (Brand/model/bios version) and so.

Also any messages. (try entering safe mode and viewing the logs in event viewer)

Is it newly built and buggy or did it work fine before?

Crushing at BIOS settings exit makes me suspect of hardware incompatibility. Need more info.

Ok. Thanks for replying Chaky. The computer has worked with no problems since a year ago, when it had a similar problem. I built it two years ago, so I doubt there's a hardware incompatability problem. I can't check messages because when I try to enter safe mode the computer doesn't crash-the screen fills with commands and it freezes. The system has an Intel Pentium 4, 3.5Ghz Processor with HT technology and a system bus speed of 800Mhz. It has 1024Mb of Dual Channel Corsair RAM. The Motherboard is an Intel D875PBZ version AAC26680-303. The video card is a Radeon X1600. The BIOS Version is BZ87510A.86A.0106.P2Z.

If the system has been working for 2 years without reinstalling XP, it's no wander that windows chrushed totally. What you need to do is reinstall the windows. Your last post make it sound like windows-related issue. Maybe corrupted registry or vital system file or wrong driver beeing loaded.

How do I uninstall Windows if I can't get into the operating system?

To REinstall the windows you need to boot from windows instalation CD. To boot from CD you need to change boot sequence in BIOS settings. Don't need to be able to got in to a OS, hell, don't even need to HAVE one.

GAH! I just found several resources for fixing my problem; it turns out that windows resarting just before the logins screen is common; it's caused by a missing or corrupt Kernel32.dll file. The website(s) I found all said to follow this course:

1. Start the Recovery Console. If you do not have the Recovery Console installed, start it from the Windows XP compact disc (CD). To do this, follow these steps:

a. Insert the Windows XP CD and restart the computer. If prompted, select any options required to boot from the CD.

b. When the text-based part of Setup begins, follow the prompts; choose the repair or recover option by pressing R.

c. If you have a dual-boot or multiple-boot system, choose the installation that you need to access from the recovery console.

d. When prompted, type the Administrator password.

2. At the command prompt, type "cd system32" (without the quotation marks), and then press ENTER.

3. Type "ren kernel32.dll kernel32.old" (without the quotation marks), and then press ENTER.

4. Type "map" (without the quotation marks), and then press ENTER.

5. Note the drive letter assigned to the CD-ROM drive that contains the Windows XP CD. It is displayed in a format similar to the following: D: \Device\CdRom0

6. Type "expand <drive>\i386\kernel32.dl_" (without the quotation marks) (where <drive> is the drive letter of the CD-ROM drive that contains the Windows XP CD), and then press ENTER. For example:

Expand d:\i386\kernel32.dl_ <ENTER>

Note the underscore character after the "L" in Kernel32.dl_

The following message appears: Kernel32.dll, 1 file(s) expanded.

7. Type "exit" (without the quotation marks). The computer restarts.

8. Remove the Windows XP CD and start the computer normally.

But when I get to step 2 and type cd system32, the Recovery Console says "the path or file specified is not valied". Any ideas?

If system32 directory is corrupted then it is the cause of your problems.
Instead of step 2 try typing "CHKDSK" to fix the HD errors.
After it has done proceed with step 2 and forth.
If you still get the same message, try typing "CD WINDOWS" (where the "WINDOWS" is the name of the directory where the windows are installed) and the step 2 and forth.

If all that fails, you definitely need to reinstall the windows.

If you don't have any valuable data on your HD, I suggest formating the HD (C drive). If you do have data you can't afford to lose, when prompted, select the "leaving the file format intact (no changes)" option. And make sure you use SAME windows directory as the previous installation. Only windows system files will be overwritten, leaving oater files untouched.

You will have to reinstall additional software you need, service packs and updates all over again.