So after five hours of arguing with my web server people, who kept sending me meaningless "error reports," and telling me it was my fault that this site and Bigindoortrains.com/forums were both down, I finally got a fellow who admitted that they had screwed things up on their end during a software upgrade, and they were "already" fixing it.
Both sites are back now. According to the first contact, I must have done something to break the site. According to the second contact, all I really had to do was wait for them to sort things out. But would they really have known I was having problems if I hadn't contacted them?
Either way, you can count on me to be on the phone the next time this happens, too.
Best of luck, all!
Paul