My computer is locking up

Hey guys,
I posted this in Help already, but then realized it didnt belong there so i'm posting it here instead (sorry!)
My computer has been locking up a lot lately, last night it locked up three times within an hour, and its happened twice today. First Firefox becomes unresponsive, and then so does Windows Explorer. I cant minimize or expand any of the windows i have open at the bottom, and i cannot open the start menu to restart or shut down the computer so i have to manually turn in off with the power button. When i try to restart windows explorer, it checks for problems and doesn't find anything, and then when i try to restart it, nothing happens and i have to shut down my computer. Any body know whats going on?
I scanned my computer with AVG antivirus and all that turned up was a bunch of tracking cookies, and even after deleting those the computer still locks up.
Btw, im running Windows vista home premium. Help please!

Nobody?

When did this start happening? Sounds like a virus or bad drivers. Is Vista fully updated?

I think it was an update that fucked everything up.
I downloaded an update yesterday, and thats when it started screwing up.

EDIT: Nevermind. I used System Restore to go back before i got that update and it still locked up on me.

Last yesterday you say?

lol yeah, day before yesterday, the 19. We think it may be firefox's doing so im trying Chrome.

EDIT: Got rid of FireFox and downloaded Chrome, no problems so far :D

Could be a virus using a weakness in FF.