A few days ago my mac wouldnt boot up. It is stuck at the grey screen with apple logo and spinning gear. I tried booting up in safe mode ala shift key but that doesnt seem to work. The Mac is probably 3-4yrs old. Just a guess. So its been through a bunch of updates. And it currently has mountain lion os. I will try booting up in safe mode again. Any thoughts or suggestions? Thanks Ps. When i try rebooting in safe mode the progress bar goes about 25%and then switches to grey screen with apple logo and spinning gear.