Kawasaki engine won't start

I have an RZT 50 mower (model # 17AI2ACP056) with the Kawasaki 22hp enigine (model # FR651VA02210 or FR651V-AS04-R) that will not start. When I turn the key the starter clicks, but does not turn over. I've replace the starter, starter solenoid, spark plugs, oil change, air filter, fuel filter, and it has a fully charged battery.

Any ideas on what I should check next?