if you want a quick solution try this:
i think ,,you must go back to the previous state where your computer working . correctly.
Start Menu\All Programs\Accessories\System Tools\System Restore
Restore your original settings. It will not affects/delete your current files, its only get back your default system. based on the date you want to. restore....
I hope it will help you...
COmmon problem ,,,like your situation is..virus affected..i think thats the only reason,,why,,..
GoD bless
-koobface^_^