It seems like something within your quest prevents the game from loading correctly. You should check if you are loading the correct spawnpoint for Geralt, if all tags are correct and if you are loading the correct partition.
If this does not help, have a look at http://www.youtube.com/watch?v=knqO4l4zBlI. This video shows how to start your quest.
If this does not help, have a look at http://www.youtube.com/watch?v=knqO4l4zBlI. This video shows how to start your quest.