So here's the thing. My 20 inch iMac (g5) won't boot. The chime plays, screen lights up but goes dark again and nothing more happens. I can hear that the dvd rom is powered (the little eject thingy plays as always) and the HD spins up. So far I've reset SMU and PRAM (yes it does the rebooting and plays chime again). I cleaned the machine and applied new thermal paste a few months ago and have a new 1.5TB disk in it. I did check machine with "yes > dev/null" in console for over an hour and temps was a lot better than before I replaced thermal paste, so I'm pretty confident that it wasn't the issue. I did have a five years insurance on it, but that went out just two months ago.. Can a dead PRAM battery make the machine act like this?