Well. Try to load into other quest.Bassically this : 
Tho if this doesnt help.Then you might have to reset the game ,of course after you do that you can still load to the previous quest.In other words the progress aint gone(most of it at least, bassically you will have to re gossip with other critters,and also get back all the stories.Tho you can also get those back with cheats :p.Bassically this:
