I just had the same problem. You might want to pull the cable off of the gearbox on the drive shaft. If you turn the cable it will run your spedo and that will tell you that the spedo itself is ok. If that works there was a small cable in that gearbox that was bad. It is about a $2 part and is fairly easy to replace. The repair shop told me that this was very common. Good luck
If that little cable is shot, find out why. Lack of lubrication to push moisture out will seize it up and cause it to twist off........ or
if the bearing behind the speedo gear is shot, the drive shaft may have shifted causing the that little speedo cable to fail also.