The variables in the problem are poorly specified. We do not know exactly what hardware you are using and have used to test with and in what combinations.
What power supply? What amprage on each rail (3.3v, 5v, 12v)? What ATX version?
What motherboard? What PCB revision? What chipset revision? What BIOS version?
What hard drive? What chipset is on the PCB?
What addin cards?
What OS? What version? What patch level/service pack?
What drivers? Their versions?
Other possible issues:
Maxtor SATA hard drives had problems with nforce3 and nforce4 chipsets.
You did not attach the molex power connector on motherboard for your video card, and your video card requires it.
If you are using an nforce chipset, NVidia storage drivers may still be buggy. Do not install them.
Your motherboard may have bad capacitors.
BTW, use Orthos instead of prime95 for dual core stress testing:
Like I said, I'd pretty much need to get my hands on the hardware itself to diagnose the problem at this point. Anyway, good luck and happy holidays.