I have an MDD G4 that has really been giving me trouble, and I'm not sure where else to look on it. Let me say first of all that I can pretty safely rule out the PSU as being the problem. I have two MDDs and three PSUs floating around, including one that is supposedly rebuilt from Ebay. I know one PSU is dead, although my two "good" PSUs will both power my other MDD flawlessly. So, as I said, I think I can rule that out as being the problem. On the problem MDD-it will sometimes power up and work perfectly. I've been able to get it running long enough to do a clean Leopard install on it, as well as download and install all the updates. Occasionally, however, it will just seemingly die. Whenever this happens, the power button will glow for 1-2 seconds when pressed, but then go out. The fan on the door will sometimes "twitch", but not actually spin up. Sometimes hitting the PMU reset or pulling the battery(along with unplugging it and plugging it back it) will allow it to boot, but at other times does nothing. I've given the whole thing a general cleaning, including cleaning the contacts on the video card and the RAM, and repasting the CPUs. I should also add that it has 2gb of all low-density ram in it. I dropped this full set of ram in my other MDD, and it worked no problems. And, just for general system information-this is a first generation "Firewire 400" model with dual 1ghz CPUs.