3) system date and time I know were correct because the computer is a laptop so old the battery no longer functions at all, so when I plug it in it makes me set date and time upon boot.
I'm almost certain that this is the problem...
avast, for any reason at any time, should be 'checked' the date and, maybe, it was incorrect set to the past... then it expired.
Once expired, changing the date should be detected as 'piracy' of avast copy...
Maybe uninstalling, booting, trying again and registering after boot.
Maybe Alwil team could help you to manage how 'deleting' this registry info from the Wndows Registry (avoiding the anti-piracy feature). I'm not sure...