I've had the game working fine before now, but I started it a few minutes ago to check something and the window just appears like this.
The full image did appear for a few seconds, but then the window just shrunk.
There's sound playing in the background, and the little I can actually see of the game suggests there's still something going on there, but I can't get the window any larger than that.
I've tried restarting the game and my PC several times to no avail. I've got a feeling switching the game to fullscreen might fix it, but I can't work out if there's any key combination I can use to do that, seeing as I can't get to the settings screen.
I'd imagine reinstalling could fix it, but I'll be thankful if anyone can suggest a quick solution.