I have a G4 (MDD), OS X 10.5, that worked fine until yesterday. Before going away for a few hours I put the Mac to sleep. Came home, moved the mouse, nothing happened. I pressed the power button, light flashed briefly, then went out and the fan blew loudly for many minutes. I pulled the plug, waited 5 minutes, replugged, pressed button, same thing. I opened the Mac, cleaned, removed battery, reset PMU. Plugged in, pressed button, same thing. Fan blows loudly, monitor is in power save mode, Mac stays off. What can I do? One year ago I installed a new power supply. I'm writing this from a local public library, so it could be longer intervals for me to respond to suggestions. But I appreciate all the advice.