After 3 motherboards, 2 different types of memory, and countless hours on the phone with abit, I can finally get into BIOS and the Windows XP setup. However, 10 minutes or so after startup, my computer shut itself off. After that, I tried waiting a little and turning it on again, and after a few minutes, it shut off. Again, I tried turning it on, and same thing, except it shut off even sooner.

Any idea where to start looking for the problem?

I'd say it was the psu right away, but the lights on both the mobo and the psu stay lit, even after the system shuts down.