prova a leggere anche
http://en.kioskea.net/forum/affich-3140 ... ot-turn-on.
poi: "I had the same problem. through trial and error I discovered if I removed my battery and unplugged it, then plugged it back in (without the battery) it would turn on. Even now, the only way I can start it is no battery, pull the plug, insert the plug and it will start. Hope it works for you, too."
"finally I can start up my powerbook G4 12" again with your suggestion [The one that worked for me was to push Shift-Control-Option-Power on the keyboard, release for at least five seconds then push the power button.]".