cub cadet rzt-s 50 wont go foward or in reverse.

I have a cub cadet rzt-s 50, i was mowing along my ditch and heard a pop. It stopped and it wouldn't move at all. Ive tried my best to follow the linkage and stuff and it all seems to be moving freely. Obviously im not much of a gear head so really im lost. Please help.

Thank you,
gregg