Hey guys, New to Mac, but I just upgraded to Mavericks and the iMac restarted. The grey screen comes on with the Apple screen and the spinning wheel. Moreover there is a loading bar that takes about 7 mins to fill from left to right. After completely "loading", the bar disappears and the wheel spins for about 10 more seconds. Then the iMac shuts off. I turn it back on and it does the same thing. None of the keyboard commands work at startup either - i.e. holding option and N or resetting PRAM. I also did the hardware reset thing where you unplug and hold down the power button, etc. But to no avail. Anybody else having this problem? Any answers on how to fix it?? Thank you all.