Since the other licenses are all being used will this show as a 4th license?
You should be able to assign licenses from your my.avast.com. So you should be able to remove the association with the system with the graphics issues.
Unfortunately, I am unable to do that. I can log in and see that I have 3 licenses, but it doesn't list the individual devices that the licenses are associated with.
Unfortunately, as an Avast Free user, I don't have a licenses section in my.avast.com, but from memory of what I had seen in the forums that function used to be available.
However, as r@vast mentions if that system isn't likely to come back on line, you should be able to activate the license on a new device.