If it's doing nothing, first thought is safety switch. Second thought is electrical.
Did this problem just pop up?
Are you sure battery is good?
Make sure PTO is off. I always hit my lever - only takes a little to trip PTO safety switch on mine.
Rock the HST pedal while trying to crank it. Sometimes the HST pedal safety switch gets a little gummed up with time.
Other switch is the seat switch....make sure it looks/acts okay.
Do you have any noises, lights at all, dash, headlights, etc., or is it just plain dead where it sits?