I am having a problem with starting the iMac today. When I try and restart or boot into bootcamp with the option key, it locks up at the grey screen. No spinning beach ball or anything. It just stays grey. The only way to restart is to press the power button. Everything has been fine and I am at a loss. It is a crap shoot if it will boot up. Once it boots up into OS X or Windows, everything is fine. Any thoughts?