Long story short, I leave the Jarl's hut after she tells me to go kill the master vampire, the townspeople are there with their torches, but talking to them does nothing. If I go to Movarth's lair, I can only go a little way in before a ledge which should be there for me to go further is missing (I have done this quest a few times before, I know it should be there). If I go back to Morthal to try and talk to the people again, they aren't there - nor are they in front of Movarth's lair. I have no way to go further, and the townpeople who are supposed to go to the lair with me have vanished. Not only am I missing almost the entire population of one of Skyrim's few "cities" (and I use the term loosely) but I cannot complete the quest needed to get the Morthal house.
Help?