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). If, for any reason, you can't run it, try booting in Safe Mode
and doing it from there. Anyway, boot after that.
5. Run the avast! Uninstall Utility saved on 1 in Safe Mode
. Boot after you've run it. Repeat this for any major avast! version you have ever installed/upgraded in your computer.
6. Install avast! using the setup saved on 2. Boot.
7. Register your free copy or add the license key for Pro. Or even upgrade
your key from old versions.
8. Check and post the results. If, for any reason, you did not solve, try doing the step 3 in Safe Mode anyway.
More info about resending licenses:
Resend purchased license: http://www.avast.com/en-eu/resend-license-paid.php
More info about registration: https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1073