Swinny,

Do you have your computer set to download Windows updates automatically?
Sometimes a patch or update from Windows can cause this to happen.

Make sure that Windows is updated with all the critical patches in place.

Run a repair of Avast by using Start/Control Panel/Add-Remove and clicking on Avast.
Look for the Option to repair. Click on it and let Avast run a repair. You must be connected to the net so Avast can look for and download any files that it sees it needs.

This is the only thing I see that you have not done.

Good luck.