Your screen shot seems to show you're in the right spot.
Did you kill the dragon a previous attempt and forget about it (just double-checking)?
This --might-- be a simple case of map loading error. Typically those are fixed by reloading the map. Make a back-up save, than do a forced map reload. Either load a game outside the area (step outside, quick save, reload, reenter dungeon; or stay at an inn). Use the back-up save if that makes things worse.