Thank you for everything. They did help, and the site is back where it was before it blew up.
It was a rouge .htaccess file in my home directory (above public_html). They renamed it. I didn't even look there. I have no idea how that happened just by making a backup, but you can be sure that I won't try that again with this plugin on 3.1.3! :)
I had already removed everything and reinstalled a fresh copy of WP, so I put everything back per your instructions, and it's all good now. Thanks!
Rouge .htaccess file contents...
deny from all
... just like you suspected, but in a different place.
I'm going to spend today making progress getting some of the rest of the content and up and trying to finish the site. I was about to install a couple of new plugins when I tried to make a backup first--just in case a plugin caused a problem... lol :)
Have a great Memorial Day if you are in the US--and a great week if you aren't! Thanks again for all the help--I learned a lot and got a lot of comfort from you being with me through that ordeal!