My IMac G5 wont start up and i checked and the power supply and logic board are both working fine. First it would just go to a blue screen when i started it up, so i put in my restore disc and went to disc utility and wiped the hard drive then tried to reinstall OS X but the installation got to 75% and then the computer just restarted and now when i try to turn it on it just stays black and i cant boot off the disc. PLEASE HELP