I have a grape iMac that won't startup. It seemed the pram battery needed to be replaced. I did(waited a full 20min, before replacing the old with new). Zapped the pram, and still nothing. From here I opened it up again and pressed the Cuda reset button...It booted right up. Everything thing ran smoothley and normaly, shut it down for the day. Tried to boot it up again the next day, nothing again. I have found the reset button trick will work everytime. Its a computer that I hardly ever use(its very jealous of my fp G4 Imac) so leaving it on all the time is not an option, but neither is having to press the reset button every time.