I have a G5 2.5GHz Dual with a problem. If left off for while, boots up, works normally for about 5mins then goes to sleep. istat shows fans at full speed, processors around 80 degree temp, when gets to around 90 degree, shuts down. Then usually does not even show video screen when booting up next time. Blank, full fans. I think is a power supply issue? If video card taken out and booted, fans do not go full power. Could it be power supply no longer outputting enough power to handle all normal functions? The fact it can boot and work normally for short while, to me would say is a full working Mac, but without enough power to function over time? According to istat, the processors are constantly at a very high temperature. There do not appear to be any leaks in the liquid cooling system. Have re-seated RAM, video card, reset PRAM. I am looking at getting a new power supply for it, but want to sure I'm not completely wasting my time. Would there be anything to indicate is logic board or processor issue?