When my son's computer is turned on it just goes to grey screen.. I've tried a number of troubleshooting things...starting while holding "c" to boot with install disk...starting holding "shift" for safe boot. I did the PRM (?) reset thing holding Apple-option-p-r keys while starting and that did add the start up chime...before it would just go to the grey screen, no chime no spinning wheel...but still no boot. The computer is still under warranty but soonest appointment at Apple Store is 3 days from now!!! Any other ideas???