Hi - When I turn on my computer, the wheel keeps spinning and stops on the grey apple screen. If I leave it there for a few minutes, the fan gets really loud. I tried pressing Apple, Option, P, R, but it only chimes once. I also tried holding down shift and restarting. And I tried holding down option and restarting. I even tried to take out the memory and put it back in. Nothing is working. Any ideas? I have the startup disks, but I don't know how to put them in the cd drive. Since the computer won't boot up, I can't open the tray. Any ideas? Thanks so much!!!!