It's official - my camera's broken.
In aperture and shutter-priority modes, it won't come out of the lowest setting, although it will still meter for it. It still works in program modes. Anyway, a half-broken camera is a broken camera, so...
Maybe there's something I can do with firmware? Whatever - somebody's trying to tell me something. I'm writing in on an old Windows 95-enabled PC at work, with no laptop, borrowed money for a new computer, and a broken camera.
What the hell did I do?! Damn.
Update: It was the CF card, not the camera. Working fine after removing the card and changing it.