i cant turn off my computer

i have 8.04 and recently after i restarted my computer due to a large update, i cant shut off my computer the normal way now. when i click on the button at the top right corner of the screen to get to the turnoff menu, it just disappears and then nothing else happens. i have tried almost everything i can think of (just converted over so that doesnt mean much), i have tried upgrading through the terminal, and that shows no probs. maybe if there isnt a solution to this, is there anyway i can do something like a system restore on it like the function in windows? plz help, i dont want to have to reinstall everything

also, i think this is a side issue caused by the main "off button" issue, now firefox is on the fritz, it lost all my favorites, the addons are gone and when i try to go to the addon menu, the whole thing just shuts down.