Hey, so the issue's been resolved! Unfortunately, I'm not 100% sure what I did to solve it. I checked my drivers, but apparently they were already up to date prior to the glitch, so I don't think that was what did it.
All I can think is that I went back to the beginning of the area (not the beginning of the quest, I just physically walked back to the beginning of the fortress) created a new save in that location, and then loaded the new save (does that make sense?). So I'm thinking that maybe it was just creating the new save that did it?
I also had my resolution turned down to 70% or so. Don't know if that made any difference (I'd already tried unsuccessfully on a lower resolution) but I suppose if anyone encounters this problem in the future, turning graphics down couldn't hurt.
Sorry I can't provide a more concrete answer, but thanks for your help! I'll let you know if any other problems arise.