Some other had a similar problem. For them the solution was to skip this quest for the moment and proceed to Whiterun. There you will get a mission which will send you in the same are (I don't wanna tell you more). At this point the dungeon was fine for them. Personally, I didn't had this problem.
Alternatively, you can try to delete and reinstall the game data (not your saves!). For some guys with map problems (some ares didn't work, i.e. wasn't there) this fixed that specific issue.