I was doing the quest for the theives guild where you go to Inkingrad, anyway I got into the second level of the dungeon and the fram rate dropped so much it froze but the music was still playing. Before I entered the place i had a follower with me that was forced to stay outside becasue of the quest i don'ky know if that is causing it but maybe.

It's a known problem and has happened to many of us. It probably has more to do with the amount of npcs inside where the game just struggles to handle all of them at once. I found that once enough falmers were killed, the frame rate speeds up a little. Oh and be sure to save after each encounter because freezing may happen further down as well.