Help! Last night I left my computer to copy a bunch of files from an external HD to my iMac. I tried to click on things but nothing worked. My mouse moved but that was it. It was locked up. Rebooted and it got past the grey Apple screen with the spinning cursor to the grey Apple screen with nothing (just before it boots into Mac). Stuck. Turned it off and tried again. Same thing. Unplugged it for a few minutes. Same thing. Held down the power button. Same thing. Booted into the repair screen and repaired permissions. No problems... BUT it locked up right after repair. I had to hold the power button to get it to reboot. Right now it is stuck on a grey screen with a spinning beach ball. HELP!