I’m not giving up helping/trying to solve it that easily :wink:

  1.   Click on Start, run, type services.msc and hit enter to open it.
    
  2.   In Services Console window, find and locate Windows Installer service.
    
  3.   If the service is stopped, start the service and set it to “Automatic” or restart the service if it is already started.
    
  4.   Reboot your computer and check if it solves the problem.
    

Ps:
This is a Windows problem and not a avast problem.