Computer not booting from HDD or CD

Hi, I turned on my brothers computer the other day to be greeted with the wonderful BIOS screen. On the right hand side in big red font, it said that the CPU had been re-installed. I thought nothing of it, thinking perhaps someone had reset the bios, so I hit exit without saving changes and tried to load windows. It goes past the first screen where it checks the hard drive, the cd-roms, and the memory. Then on the next screen it freezes indefinitely. After leaving it running overnight, there was no error message. At that point I reset the bios to default settings, and tried it again - Same thing. I guessed maybe the windows install had become corrupted or something, so I popped in my XP disc, and it got to the same screen it freezes at. At the bottom, the message "Press any key to boot from CD" as usual. I pressed spacebar, and saw the standard "setup is inspecting your hardware..." There, it froze again. I left it for a few hours and no luck again.

Just to be sure the 2 month old HD wasn't failing, I popped it in my computer, copied about 2 gigs to it, and it seemed to work fine.

At this point I'm not sure whats up with it. My only thought is that
A) CPU is damaged in someway, maybe it overheated?(New desk so it doesn't have the same air circulation it had before)
B) Something wrong with the motherboard, maybe a virus or just something worn out.

Not sure what exactly is wrong, but any ideas would make it a lot less painful(and expensive) in figuring it out.

Its a fairly old custom-built computer,

Socket 372 Celeron
Im not sure of the motherboard unfortuneatly, but it is asus with via chipset
512mb SD Ram
ATI Radeon 8500 Pro 128mb (AGP 4X)
Soundblaster PCI card - again, not sure specifics
250 gig maxtor hard drive (less than 3 months old)
Lite On 16X DVD Burner
HP 4X CD Re-writer

If any other info is needed I can get it

Thanks in advance,

Matthew