When I looked under the mower, it appeared there are 3 belts. The mower deck belt, the drive belt and a belt above the drive belt. It was late and hard to see but I could feel a belt. Is this correct? I didn't see three belts on parts diagram.
Also, should the drive belt be spinning while the motor runs. It is not. Also, when I release the brake and drive F or R, nothing engages the belt. That must occur at some point. As you said the engine spins the tranny pulley via the drive belt. This is not happening.
FYI - The PTO does engage the mower blades and they run very well.