Download the AVG Removal Tool (ART) from here
(make sure you get the appropriate version) -> save to desktop.
Boot into SAFEMODE - NO Networking. Then go to desktop, RIGHT-click on the ART icon and select Run as Administrator.
When complete - re-boot.
Install MS Security Essentials --> http://www.microsoft.com/Security_Essentials/
Then reset the Windows Firewall to its default settings -
START -> type cmd.exe
-> right-click -> run as administrator -> type netsh advfirewall reset