Have you recently downloaded or installed SP2?
If you have, Microsoft has free tech assistance for those who have been deleteriously affected.
Microsoft Security Product Support Policy
Technical support is available from Microsoft Product Support
Services at 1-866-PC SAFETY (1-866-727-2338). There is no
charge for support calls associated with security updates.
International customers can get support from their local Microsoft
subsidiaries. Phone numbers for international support can be found