After the system restore, your system will be in an inconsistent state (I guess), with files of avast left behind...
I suggest an installation from the scratch:
1. Download the latest version of avast! Uninstall Utility
and save it.
2. Download the latest avast!
version and save it.
3. 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. This is important
. Anyway, boot after that.
4. Run the avast! Uninstall Utility saved on 1. If, for any reason, you can't run it, try booting in Safe Mode
and doing it from there. Anyway, boot after you've run it.
5. Install avast! using the setup saved on 2. Boot.
6. Register your free copy or add the license key for Pro.
7. Check and post the results.