Are the jaws all the way open or closed? I would try taping the jaws a little in, try it, then tap them out a little and try it again. The back plate has a sprial cut in it to catch teeth in the back of the jaws. As the backplate is turned by the key it moves them in or out. If you can get it moving and get the jaws out, make sure to number them or watch what jaw goes in what place. The "gears" are cut on the jaws at a different starting point so they all meet in the center.