I got Avast to complete its Full Scan.
Thanks for the tip - the progress meter took seven hours to complete.
So I am satisfied now that it can do a full scan, in any event that I should need it.
It is disconcerting that it took an hour and a half to reach 1% - I dont remember it being like that before, but I am most please that it was able to accomplish the task.
It is so unusual that a progress meter would stay at 0% for so long, as it does actually look like it is not working at all. Thank the Forum for its help.