G5 20" iMac randomly turns off

Hi, got another g5 20" iMac this week..

This one works fine for hours sometimes, then randomly just turns off..
Other times it shuts down after a few mins.

I've looked at all the caps on the logic board and the psu, and there is 0 visually faulty ones.. They all look 100%

Ive stress tested CPU, getting it up to 80c and it still runs ok... Then randomly during normal use it just dies, like power has been removed.

I have another g5 psu here.. It's not iSight model, but I'm thinking of putting it in to see if it fixes the problem.

Do you think the hard drive could be the problem? It feels very hot.. But system doesn't shut down or anything.. Just goes off.

Any info appreciated..

Paul

You should try Apple Hardware Test.
Replacing the power supply is also a good troubleshooting step.

The Apple Hardware test might find something so I agree!

Is this that last 20" iSight model with 2.1Ghz G5? Mine had a bad cap in the power supply and did that very thing.