What we need to do is reinstall Avast (there should be no problem this time)
Download Avast Uninstall Utility to your Desktop.
Download the correct version of Avast
Avast Free
Avast Pro
Avast Internet Security
Avast Premier
Disconnect from the net
Uninstall Avast via control panel
[]Run the uninstalltool and accept the reboot to safe mode
[]Once complete reboot your system
[*]Reinstall Avast