Craftsman Lawn Mower Won't Start?

I am trying to help my dad with his mower. He bought it used last fall and it has worked fine until today. He was out mowing part of his field and he said it died, he tried to start it while the blade was engaged, he said it back fired a couple of times then nothing. When I try to start it, the flywheel barely turns. I took the cover off of the flywheel and tried to hand turn it and it will only move about a quarter turn and freezes. Oil and gas levels are OK. I tried to jump start it and nothing. Any help would be appreciated.

By Marcie W