Sounds to me like game was unable to find the data for Dead Money. You can uninstall and reinstall it, but since you already loaded the game without the Dead Money data all your progress was probably erased. Your best bet would be to reload an earlier save from before the save you previously loaded. Hope this helps, sorry. If you don't do the 1.5 update your dead money stuff will still be in your save. How ever i can't get honest hearts to start either with the update or without.