My grandstand will not start changed starter and battery and ignition still will not start. If I cross the starter with screwdriver it starts right up! What could be wrong with it?

If you have a multimeter you can test voltage on the small wire at starter solenoid. This triggers the starter solenoid to bridge the starter solenoid to starter side when 12v is achieved. So you will test that wire while trying to start mower. If you have two small wires at the starter solenoid then one is ground and other is 12v