Alright. First thing I would do is remove any unnecessary hardware devices (internally and externally). Internally, remove any PCI cards inside the PC, but keep your graphics card in if your using once
. Externally, remove all devices connected to the PC apart from your keyboard and monitor.
Boot the PC and if the problem occurs again, then power off the PC, and clear the BIOS CMOS by removing the lithium battery from the motherboard for a minute or two, then placing it back. Power up the PC again and see what happens.
Failing that, the next thing I would do is to check the hard drive for any errors. You'll need a Windows XP Setup Disc for this. Place it in the drive. Power up the PC, and go into the BIOS settings. Make sure that your CD-ROM drive is set as the primary boot device. Save any changes made in BIOS settings, then restart the PC...
...Then, when prompted to, press any key on the keyboard to boot into the CD. Once loaded, select to enter into the Recovery Console
. Log into the Windows partition, then at command prompt, type chkdsk x: /r
is the drive with Windows installed.
If you don't know the drive letter, it should be displayed at the top of the screen as x:\Windows\
as the logon partition.
Failing that...post back