If it's really the update you can remove the corrupt update, shut down your PC, boot it and keep hitting F8 until you get to Startup Options menu (if you see Windows screen restart and try again) then it should work. When it works go to Programs and Features>Remove Programs>View Installed Updates. Remove the update as you are uninstalling a program. Restart.
However, if it went deactivated you should better have the key of it. Re-enter that one (should be on a sticker down on your PC) and it should work, ot use phone activation (some countries stopped doing this for win7 but try your luck)
However, if it was a crack it's a chance that it got busted, and you'll have to buy a real key.