I'm no guru but I've been to the fair a few times. LOL Check your voltage to the solenoid and voltage to the ignition coil. If your coil is bad the ski won't start, it will still turn over. You can unplug the wires from the MPEM that go to the rear of the ski. Put a volt meter on the wires, push the start button and observe what happens. If you are getting voltage to the rear electric box then you have a component failure in the rear. If you are not getting a signal to the rear box then your issue is up front.
I''d check the Dess Post, and start switch. Push the button. What happens when you push the start button without the key inserted?