Ok. So lets eliminate things one by one,
Battery, assuming its good and cables are CLEAN on BOTH ends including where it bolts to frame.
Small wire that connects to starter is snug, not overtightened and broken inside.
This wire typically passes through clutch switch before connecting to starter.
By jumping from battery cable connection to this small terminal (tractor in neutral) engine should turn over.
If the first things mentioned are good starter should crank.
If it cranks, then we can assume the clutch switch or ignition switch and related wiring is faulty.