There is a hydraulic valve that sits at the bottom of the steering column just in front of it that has a cable coming from the clutch pedal to it. If that cable gets kinked or something is preventing that valve from closing it will prevent the tractor from moving. Also I once washed my tractor and got the computer box wet that sits just behind the base of the steering column and my tractor wouldn't move for 2 days then finally after it dried out everything was fine again. Needless to say that box and the solenoid on the shuttle shift are protected with a thin layer of rubber mat slid over the shifters any time it's raining and the tractor is kept inside.