Originally Posted by THGhost
I've seen other people post similar screenshots and have their problem solved in the past. ...
That's because those screenshots actually contained an error message hinting at the cause of the problem, yours doesn't (it seems you've shot before the actual problem occurred).
At any rate, try launching jk2 in safe mode (from the start menu); if that works, your problem is probably easy to remedy.
If it doesn't, maybe you'll have to downgrade the video driver (I think quite a few people have had problems running jk2 on ATIs with more recent video drivers).
But first things first.