I didn't change the file system. Should I?
No. It's just that if you have done, the registry key will be
lost and you'll have to add it again.
I suggest an installation from the scratch:
1. Uninstall avast from Control Panel first.
2. Boot.
3. Download the latest version of
Avast Uninstall and use it for complete uninstallation.
4. Boot.
5. Install again the latest
avast! version.
6. Boot.
7. Check and post the results.