After the said "repair"...did you get all your service packs and updates....
because file\dll versions may be the issue.....
As mentioned...sometimes the fastest...and most efficiant way to fix is FNR ( I like that ;) )...or format and reinstall
Yeah, morganlefay, "FNR" is some "Dell rollout" vernacular. ;)
windows update requires BITS to be running
start > run [services.msc] > Background Intelligent Transfer Service - double click, and set it to run automatically
as for the AV :
do you have another version around ?
even an 'old' norton 2002 ?
try and load / run that
it COULD be baddies that stop you running
it could be op/error
it could be bad luck