your PCP&C 510 might not be able to power the 8800GTX's in SLI. The 8800GTX might over draw the 12V rail. Assuming each 8800GTX draws the full 225W at full load (that is the maximum power draw a card can have, 75W from the slot, 75 from each 6 pin connector, you have a max of 225W. Anyway, graphics today use the 12V rail...so divide watts by voltage to get amps. So...18.75A per card...that's some insane power draw. Anyway, you might need a new power supply either way.