Need help

I have undetermined problem which makes me insane. My computer crashes during ALL games, including old 2d stuff. Sometimes even in some applications. Applications ranging from Itunes replacements like ephpod to rocket dock. This is NOT a software issue. The problem persisted even after full format and on freshly installed Windows. RAM modules are OK. HD is clean. No infections. CPU temp is normal.

The graphic card is NOT the problem; I tried several and the problem remained.
Here is the list on my hardware.

mobo: ASRock P4VT++
PSU: Codegen 300W (the problem remained even with an old Radeon 9000 with 64mb; don't think it's dying.)
CPU: Intel Celeron 2,4 Ghz
CPU fan: Zalman
RAM: 768mb, all modules are the same brand name/speed
HD: Hitachi Deskstar 80Gb
Card: ATI Radeon 9600 XT with the latest Omega drivers
OS: Win XP SP2

All drivers are installed; NOD32 is defending the machine.

Please help. I don't know what to do. Thank you for your time.

OP here

Everything worked fine before the problems occured so Win XP isn't the problem.

I would say the motherboard might be the source of my torment. So, apart from my inability to attain Vista unless I torrent it, and borrowing a HD is out of the question because my friends would rather seperate themselfs from their limbs, I have to ask: are there any benchmark applications I can use to pinpoit the faulty component?

thx for the help :)