So your cranking circuit has failed
To protect peoples feet no mower engine will crank with the PTO engaged
To prevent the mower taking off & running down you can not crank it in gear or without the parking brake on
Different companies do this different ways & I can never seem to get my hands on the right Grasshopper circuit diagrams.
You check the circuit by testing for battery voltage at the solenoid trigger wire when the key goes to the S position.
If it is a piggy back e then there is one thin wire on a spade ( push ) terminal
If it has a remote solenoid the there will be 1 or 2 wires at the base. one must got battery voltage and the other must go ground to crank the engine.