Try a clean install.
http://files.avast.com/iavs9x/avastclear.exe
Download locations
http://files.avast.com/iavs9x/avast_free_antivirus_setup.exe
http://files.avast.com/iavs9x/avast_pro_antivirus_setup.exe
http://files.avast.com/iavs9x/avast_internet_security_setup.exe
http://files.avast.com/iavs9x/avast_premier_antivirus_setup.exe
Download and save the uninstaller (avastclear).
Download and save the desired version of avast.
Run uninstaller for each version of avast you have “ever” had. You will be prompted to reboot into safe mode…do so.
Reboot.
Install avast.
Reboot and register. 