G4 Quicksilver - Power problem?

[ucganka]

I have a G4 Quicksilver that has an intermittent problem. It crashes after it has gone to sleep, but never when im around.

If it goes to sleep and check on it every 15-30min later...fine - no problem.

But if i leave it and say come back an hour later i find the machine is switched off and upon restarting it has reset its date to 1970.

Steps i have taken:

I first tried resetting the PRAM Battery (P-R-ALT-APPLE)
Changed the PRAM battery
Reset the Motherboard after unpluggin the power cable

The machine had all 3 memory slots used so i used just one memory at a time - same problem!!

I removed the IDE Hard Drive and fitted another to eliminate software from hardware problem - again no change.

Am I experiencing a Power Supply or Motherboard fault??

Please help...i am at my wits!!!

Kind regards and thanks in advance

Naved