When I got this PowerMac G3 266 MT w/ G4 500mhz processor)from eBay, the computer was running without any problem. It had only OS 10.2 installed in the hard drive so I
started format the drive (two partitions) and installed OS 9.1 first and then went to install 10.2 to the second partition. And then computer went off all of sudden. The fan was running but the LED light (ON/OFF power button) was off. I tried to restart but the keyboard wasn't working either. Everything went dead except of the fan running. That was it.

Next day, I changed the battery on the logic board to a new one and reset the CUDA button and reseat the RAM (actually I took two out of three modules out of the sockets) but none could bring the power back to the computer, except this strange phenomenon. When I turn the computer next morning, the power came back! But only for a few minutes and went off again. And this morning, the power came back again for while (about five minutes) and went dead again. Does this mean instability of the power supply or the logic board or the processor failure? Any idea