|Your power culprit COULD be the power supply. I recommend not to use the PSUs that come with cases, unless Antec or another "good" brand. Even though the amperage on the 12V rail(s) may be high, sufficiency and power output at load may not be.|
Another possible culprit could be the motherboard. Motherboards going bad cause similar problems, and that could include a corrupt BIOS.
Try to flash to a current BIOS and see if that helps. If not
try swapping out the PSU to a (proven) reliable power supply.