I bought a Power Mac G5 online (Dual 2.3Ghz) and got it up and running with new peripherals. I installed OSX 10.4 on it, and it started up and ran fine. I adjusted the power saver settings at one point and that seems to be where the problem started. After I changed the sleep time, it never went to sleep after that. So one day I manually told it to sleep, and it did... and wouldn't turn back on. I click the reset button on the front and I hear a click, and a fan starts, the white light in front comes on and a red light inside comes on. That lasts for about 1 second, then another click and it all goes back off. I looked it up elsewhere and they suggested replacing the battery. I took the old battery out and tested it, and it seemed to be bad... the reading started out high on a voltmeter but quickly went down into the bad zone. So I put a new battery in and voila, it seemed to fix it. But I shut it down again, and again it won't boot. Same symptoms. It comes on for about 1 second and immediately goes back off. The weird part (well, one of them) is that I took the backup battery out and tried to boot it a few times, and it booted on the third try, with no battery present. So there goes my theory about the batteries. I tested the new battery I put in it and it exhibited the same test symptoms - the voltage slowly went down while connected to the tester. Then, I tested a brand new battery and apparently, all batteries exhibit that behavior - the reading starts out good but slowly goes down. So it looks like the batteries aren't bad at all, and anyway, it booted once with no battery at all. I'm beginning to suspect a power supply problem. Has anyone else seen this? Thanks.