JD L120 B&S twin. Battery is up but won't start?

After all winter in the barn, It started ok, but after one pass, the deck drive switch didn't activate the deck normally. It took several seconds to engage the mower blades. On the third pass, when I pulled the switch, it killed the motor and I can't get it to start. The engine won't spin. I adjusted the valves and pulled the plugs so I could find top dead center easier. It still turned hard. It should have spun freely without the plugs. Could it be the deck clutch? Maybe it has locked up?