Why not just uninstall Avast from Add/Remove Programs?

Than download and run the complete Avast Uninstall Utility Here: (Follow the instructions exactly.)

http://www.avast.com/en-us/uninstall-utility

Than get a fresh download of Avast at www.avast.com

Register for your license key.

It sounds like a complete removal and reinstall of the product might be needed as previous options for fixing Avast have not worked.

Jack