G5 PowerMac Unexpected Intermittant Shutdown

My PowerMac G5 periodically and without warning, just shuts down. It will start up again immediately. There are no consistent user inputs that cause the problem. Sometimes it happens shortly after boot up and at others, after hours of computing.

Things I've tried: Cleaned the interior, concentrating on cooling fins; moved the CPU to insure adequate air flow; checked all cables for solid connections; reset, tested, and bypassed the UPS; gave it a swift kick.

Set-up: PowerMac G5 2x2 running OS 10.4.

Most likely a power supply...start looking for refurbished on ebay.

Agree with the above. You might give the Powerbook Medic site a look for a replacement: Mac Repair - Mac Parts and Service for Apple Macbook, iPhone, iPad