Upgrading to 10.8.4 from 10.6.8 bricked the MacBook Air on reboot

Hi-

I just tried upgrading from 10.6.8 to mountain lion via the App Store download and it appears to have broken my computer. It went through the osx download screen before the entire screen turned white, displaying a rather broken looking blue loading bar sort of intersecting a spinning wheel animation in the center of the screen. I am afraid to turn it off / do anything in case it makes it worse. It has been over two hours now and I have work tomorrow/ apple stores are all closed in my area. Any suggestions?

Thanks!

Lkroo