Well it shouldn't need another topic as you already have one for the update issue.
It would have been better if you had actually said that the problem "black empty Avast window" was resolved in program update, effectively closing this topic and continued in your other topic which contains the information you already gave.
Personally as I mentioned:
Unless as mentioned in that topic you have "installed Avast in another drive" and I don't know why you would need to do that. What I also don't know is when the popup appears in trying to populate it, it is looking in the wrong place.
I don't know if this is the source of your problem, the only thing I would suggest is a clean reinstall into the C Drive.
