Personally i would uninstall avast and use registrar lite (freeware registry editor)…
http://www.resplendence.com/reglite
to find all instances of alwil or avast and clean the registry as well as the alwil programme folder.Something is obviuosly persisting (probably in the registry).Registrar lite is good be cause if you type in alwil and “find” it will find all entries in one go and allow you to edit delete or whatever .Obviuosly backup your registry before any alterations.Once you ve done this reboot and reinstall avast.
me