I just got an Older Yard Pro with a 20HP Kohler engine from a friend. He said it just needs a battery. Well I got a new Battery and it started, Let it warm up some and took a short ride around the yard. Tried to engage the Mower deck and the engine stalled out and now will not restart. You can hear the Selinoid and see the fly wheel trying to turn, but will not move much. I ensured the lever for the Deck engagement was disengaged, but it will just not turn over.
Thoughts on things to try?

Hi,
Check the pinion(gear) on the starter. Sounds like it may be wedged in the flywheel ring gear. Of course, did you check your oil before riding it? That is always the first thing done before cranking any of these engines; they run much hotter and are more likely to consume oil than an automotive engine. Has to do with air-cooleed versus water-cooled.
Peace,
Clarke