If the machine will not move, when set to forward or reverse position, it could be that the belt or the spline connection to the hydrostat pump is broken.
The hydrostat is the hydraulic pump, which delivers and controls the oil for the wheel motors. So if this is not working, the machine cannot move.
The spline connection is the connection between the pulley and the shaft of the hydrostat. We often see that this connection breaks.
This happens because of No grease, the grease nipple on the pulley should be greased at least once a month.