Does it happen when the dungeon has a cutscene ? I've had a similar issue before (my monitors lost all signal, I could still hear a loop of background music but couldn't ALT-TAB, move my mouse or anything everything completely froze), and the only fix I could figure out was either skip the problematic cutscene or delete the related ex1, ex2 or ex3 files to reinstall the ressources because of a file corruption.