You probably need to do a clean install…

Download and save the avast uninstall tool
Download and save your choice…
Free
Pro
Avast Internet Security
Premier

Run the uninstaller from above. You will be directed to reboot into safe mode…click “yes”.
Reboot
Install choice from above. Use the “custom” install. You may need to either de-select the “browser protection” or disable the “avast online security” add-on in your browser(s).
Reboot and either register or insert license.