Hi and Welcome!
Could you describe more detailled?
I had E-Trust anti-virus which I assume came with the laptop. I removed it to the best of my ability but I am still running into the problem of it not allowing me to download AVG or Yahoo anti-spyware. This all began because I got a virus which is now taken care of.
You formatted the HDD and reinstalled Windows from scratch, using the "recovery" media?
Blocking downloads of Antivirus and similar software is a sure sign of a severely compromised system.
"The only way to clean a compromised system is to flatten and rebuild"