G5 keeps powering up for a few mins then switches off?

Thank you for contacting Fixya Support, I am glad to assist.

There are a few steps you can try to troubleshoot this issue:

Try a PMU Reset:
* Turn of your iMac if it is already turned off
* Disconnect all connections to the iMac except the power cord
* Now disconnect the power cord for approximately 20 seconds
* Reconnect just the power cable the keyboard, mouse and power cord, and then power your iMac G5 up.

* Check to see if the iMac boots up normally without power interruption.

* If the iMac G5 shuts off again, try these steps, another recommendation would be to remove all connections including the power cord, and lay the iMac G5 on soft cloth face down and with a philips screwdriver, remove the plate on the bottom of the iMac G5 where your RAM memory is located.
Before removing the RAM however, touch your hand on the metal boot to discharge any static current you carry for approximately 5 seconds.

Now remove each RAM card and then reseat (re-install) each card.

Restore the RAM card cover with your Philips screwdriver, reconnect your power cable, keyboard and mouse and turn on your iMac G5.

See if this second procedure helps if the first procedure does not work.

Let me know if this helps.

Regards

-Mactechtrainer