After any of those actions, you need to reboot before you test the results.
So try "add/Remove Programs" -> avast -> change -> repair (or the similar equivalent, depending on your specific Windows version). Once the repair finishes, close and reboot.
If that was not enough so to solve the problem, download the latest stable version of avast (the same edition you currently used, Free / Pro / AIS) and install over your current installation (no need to uninstall for now). Once the new installation finishes, reboot and test again.
Please report back.