I would say either RAM or PSU for starters. Both are big contributors to BSOD's.
and put it on a CD/Floppy/USB stick, and then boot from it. Run it for about 4 hours and check if there are any errors. If there are errors, that means parts of the RAM are bad and you should RMA it.
Do that for starters, if the RAM checks out, come back and we'll dive deeper.