Not heard had this happen to me before, but as refuse said, try loading a save from before that point, if not try starting a new game (I know, it is a pain sometimes), if it doesn't work still then backup yuor saves and override and then re-install the game, that should do it
And as for fuelthefire, you got the wrong topic mate but here's a suggestion:
Try re-booting your pc.. you may have to clear out your cache
if that doesn't help, make sure your computer has the right requirements; try for the recommended specs if you can;
if you have any back ground processes running, shut them down so that your computer's resources are devoted to just TSL;
if all else fails, back up your saved games and anything in your override, then re-install the game.