This 'blog was off-line for more than 24 hours after an event on the server. A technician at the hosting service ultimately identified the problem as a conflict between a security up-date and the theme — software establishing the appearance (lay-out, color-scheme, &c) of the 'blog. (I find the same conflict when I attempt to use WordPress Default Theme 1.6, upon which my theme was originally based.)
I am told that the administrators can and will change a configuration of the server to allow that theme to be used; but, to get the 'blog back up-and-running in the mean-time, I am temporarily using a very different theme. If, by the time that you read this entry, the 'blog looks pretty much as you're used to seeing it, that means that I have returned to the original theme.