why does my john deere mower mower lock down when I try to start it ?

When I engage my key to start the mower the flywheel turns half of a turn and stops as if in a bind.The starter works fine.The flywheel key is not severed or damaged cause I pulled the flywheel.The crank shaft is not broken Why is it in a bind.If I keep clicking the key to move the flywheel it will start eventually, and run perfect until you shut it off and why does it repeat this binding thing.It is a John Deere Model 105 2cylinder 17 horsepower.what should I check for next.