Well, I suggest an installation from scratch.
You need to download the setup again...
1. Download the latest version of avast! Uninstall Utility
and save it.
2. Download the latest avast!
version and save it.
3. (Optional) If you want, save your avast! settings for later restoration (Settings > Maintenance > Back up).
4. Uninstall avast! from Control Panel (if possible) and reboot.
5. Run the avast! Uninstall Utility saved on 1 in and follow
the instructions. Reboot in Normal mode after that.
6. Install avast! using the setup saved on 2. Register your free copy or add the license key for the paid versions. Boot.
7. Check and post the results.
Please, be patient, boot when it's said to boot...