Well, this was my first 'real' computer when I hauled it out of the box 10 yrs ago or so. I only know a little more now than I did then - so I just googled the difference between administrator, standard and guest accounts.
I guess I've been using an administrator account (if there's a password, both the machine and I have long since forgotten it), since I've got full reign to install or uninstall anything I want -- there may be the rub!
I tried running DVDFab with the guest account as a result of your suggestion to try running it as the administrator, which I was already doing. But I thought your point was to see if another user account would be able to run it, so I tried it.
So to answer your question, I haven't tried the clean uninstall on either account since first using the guest account.
Based on what's happened so far, I don't think it's worth it to me to spend the time trying to get this system restored so I can once again run DVDFab (and I don't think I'll be buying a new machine anytime soon). But I'll bookmark this thread in case I change my mind.
Thanks to you and others for all the help now and in the past.