I have an EMC 1864 PowerMac G4 with 1GB RAM, running OS 9.2.1 and 10.4 that I am close to retiring/selling (it is not my primary computer). Sometimes when I press the power or reset button to start up the machine the screen remains black and instead of a grey screen appearing and booting it just shuts down. It typically does this a few times in a row, then it is fine for a large number of boots. Then it happens again during another boot. When it does boots up, it is rock solid. I have tried booting up from a CD and I get a similar rate of boot failures so I do not believe it is a problem with the hard disk. Incidentally I was not able to boot up from the CD by holding the c-key but I was booting into the OS and selecting the CD drive as start up disk and then rebooting but I think this was just a coincidence and evidence of the above problem.