Check your D800 diode: A) It needs to work, B) It was often installed backward, and Thus C) It causes strange behavior if it is neither.
Hint: To replace it, the black stripe goes toward the mother board.
RAM errors are common with the ZIP ram and diagnosing it requires either filling it completely up, or removing it in steps.
Test your PSU under load, otherwise the results make no sense.
Mech (Mike) of A4000T.com fame, is excellent in diagnosing A3000 screwup's, give him a holler.
