Mac won't restart after updating to OS X Mountain Lion

Like what happens? Is it just spinning?

If you've waited sufficiently long (say 10 minutes) you could just hit the power button which will do the trick. A little more gentle would be to open a terminal window (if you can) and type 'sudo reboot' (without the quotes) and enter your password when it asks. That will do it too.

i upgraded to mountain lion and find that when i go to boot up the computer initially it freezes on a blank white screen. if i press and hold the power button to turn it off and then try turn it back on again, it loads ok, but takes a lot longer thanit used to prior to upgrade. is this essentially whats happening with you? it will also happen upon restarting my mac as well!