Something may have caused a corruption in the system possibly to do with automatic updates. Perhaps updating the system to SP3 would resolve it. My advice is to complete what we're doing first and then try updating manually.
Can you post a list of your security programmes and we''ll see if any changes are required.
Ideally you need one firewall, one anti-virus and one anti-malware programme running at startup.
In addition you can add Ccleaner, Site advisor and Spywareblaster. That should be enough.
I would recommend dumping all P2P programmes as they are very susceptible to malware.