Then speedlight locks to the hot shoe by means of a small pin attacked to the lock lever that goes down into a small hole in the front of the hot shoe on the camera.
The pin may not actually be retracting when the lock lever is turned to the left to unlock the speedlight, which would also mean it is likely no longer connected to the lock lever.
If so, there is no way Nikon can fix it over the phone. Your camera is probably no longer in warranty, right? What about your SB-600? Is it still in warranty?
If not, you can take (or send) your camera to the nearest/any camera shop that can do repairs.