I suggest an installation from scratch:
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 Windows in Safe Mode, uninstall avast! and then reboot in Normal Mode again.
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...
Do you use any other antivirus or security program in this computer?
By the way, this forum is for avast! account and not for the antivirus itself.