An easy way to see if the cable and speedometer are OK is to disconnect the cable housing from the trans. and spin it with your fingewrs and see if the speedometer hand moves, or connect the cable to a variable speed, reversable electric drill and turn the cable that way. If the speedometer doesn't register you know to start checking the cable or the speedometer head, if it works then the problem is in the speedometer gear, either stripped, cable not engaging in the gear, or the transmission gear is loose on the shaft or stripped.
It should not be to hard to find the problem.
