Small Engines (Lawn Mowers, etc.): Craftsman 16.h.p. garden tractor, blowups, garden tractor

Question
Can you tell me why my tractor will not move when I put it in gear and release the clutch?

Answer
The two simplest possibilties are that either the belt is off or broken, or that the brake is stuck.  Does the engine lug or change
its sound when the clutch is released?  Can you push the tractor?

 Look at the belt, and also find the model numbers off of the tag
under or behind the seat, and I can look at the blowups to see
what model you have.

  Thanks,
Fish