Computer starts up to white screen
My iMac starts up to a white screen and stays that way and won't start.
iMac, Mac OS X (10.7.3)
Hold Shift key upon boot, if you get in copy your users folder to a extenral drive as soon as possible and disconnect, do not use TimeMachine you can set that up later.
https://discussions.apple.com/docs/DOC-3046
https://discussions.apple.com/community/notebooks/macbook_pro?view=documents