I am surprised you didn't call MS tech desk first. They have that under control.
And anything to do with MS updates is covered FREE from MS even OEM versions of Vista.
Anyway go to the following and try the fix near the top by "Deepak Gupta" first then
if that fails to help, near the bottom by "cal me hal" is how to create a batch file
that resets the permissions for you.
http://social.technet.microsoft.com/Forums/en-US/itprovistasetup/thread/95edbee4-a75c-48ad-91d1-5316a96f9567