It sounds as if you need a wiring diagram for your mower. The brake and seat micro-switches are often not the only ones (there is often a fuel contamination sensor on the carburetor, for instance). Since it does not crank, there is a break in the starter solenoid circuit, most likely due to one of the micro-switches not closing. This could also activate the ignition kill circuit. In other words, there may not be anything wrong apart from a wire off a micro-switch, or a broken micro-switch, as Bruce said. To sort this out you need to either trace the switches on the wiring diagram, or find someone on this site who is extremely familiar with that wiring diagram and can guide you through it.
