Mac stuck installing update

Started doing an update on mountain lion last night and it is still running this morning. Appears to be stuck...says safari and itunes producers are being installed and not to restart. I tried to restore back before the update via time machine, but it wont let me? I do have time machine back up if needed. Should I go ahead and force power off the machine and then restore from tome machine. Dont want to wind up with a corrupt drive from stopping an installation?