Just uninstall from control panel, then run Avastclear: http://files.avast.com/iavs9x/avastclear.exe Cleanup Tool
If there is no folder in Programs just choose none, then run it and reboot.
Then you can install Avast again: http://forum.avast.com/index.php?topic=147778.0 Avast Download
Be sure to choose custom and untick everything unneeded.