InMotionHosting responded to my support e-mail – turns out they’d suspended the account because of some spurious .php code that was threatening to crash the entire server. They’ve reinstated the account, so that’s good. And the .php code? Well, I’d been playing around (unsuccessfully) with their MySQL database option and I think I screwed it up. That’ll teach me to not start building a MySQL database before I know anything about it.

So the reason for the website being down was my fault, not theirs… Go figure. 🙂