More commonly, a broken cable is the culprit. You will need to check the external things first such as that you have input to the transmission and that the wheel clutches are both in order. You can remove the drive shaft cover at the rear of the engine with a 5/16" or 8 mm socket and extension to check out the shaft. If it is inside the transmission, it is likely to take extraordinary measures to repair.

Appreciate the advice.Thanks!