My service host moved this web site to a new server. In the process, they messed up the database in a very subtle way. Everyone using the default color theme (ie all of you who were members before last week) crashed and burned but people creating new accounts could log in and write messages. Most significantly, I couldn't log in to try to figure out and fix the problem.
Eventually, by creating new accounts and muddling through the site, I accidentally found the problem and have at least made it so we can all now log in again. Getting the site back the way I want it to look may take a while.
Sorry for the trouble. Unfortunately, since the site seemed to work for anyone who wasn't a prior forum member (including my service host), my service host assumed it wasn't there fault and they were no help whatsoever

I can't say exactly what happened and there is still a possibility that there's more damage to the database that I am as yet unaware of. Keep your fingers crossed.