PowerMac won't stay powered down

[bobschwenkler]

I have a G4 Dual 1Ghz Quicksilver. As of recently it won't stay powered down when I say "Shut Down" in the software menu. Restart works fine, everything else is normal. I can power it down by holding the power button for a few seconds, but cannot start back up simply by pressing the power button again. I have to remove power from the computer (unplug it) and reapply it a few seconds later. Once I plug it in it begins to reboot on its own before I've even pressed the power button.

I tried resetting the PRAM. Seems like a hardware issue, bad switch somewhere perhaps. Any ideas?

 

[Frisco]

Sounds like a bad Power Supply Unit.

 

[MacNut]

Sounds like something is stuck in the on position in the supply.

 

[MacsRgr8]

Have you removed all 3rd party hardware stuff which is physically attached to your Mac?
USB peripherals can cause weird power problems in my experience.
Also remove any 3rd party PCI cards too.