you need to replace the cylinder what has happened is the cog in the cylinder that rotates the locking mechanism has moved from the postion it should be in. take the cylinder out, all you need to do is undo the screw from the side of the door and then u will need to turn the key to remove the cylinder from the door take it to your local locksmith and get a new one should'nt cost much more than 15 quid
matt
February 2007