The firmware update takes a while - but shouldn't be any more than 15-20 minutes, tops. Boot into your Recovery partition (hold down the command and R keys whilst booting) and if you can get that far, try rebooting again.
Same problem afterwards? Call back...
EDIT: I realize that I may have misunderstood your problem - do you see the update in the App Store and you've already installed it?
Message was edited by: clintonfrombirmingham