My PowerMac G4 will sometimes fail to wake from Sleep. The system will be at the login screen, asleep, and I'll either move the mouse or press a key on the keyboard. Most of the time, the system comes up normally. But when it doesn't, the fans will spin up and the case status light will indicate that the system is awake, but the hard disk and graphics card don't activate; the keyboard and mouse are unresponsive. Pressing the power button makes it brighten for a moment but the system doesn't go back to sleep. I have to hold the power button for several seconds to shut off the system. I ran the Apple Hardware Test CD and no problems were reported.
