Small Engines (Lawn Mowers, etc.): riding lawn mower, lawn mower, model number

Question
The mower engine is fine it's start fine but when you put it on gear either forward or reverse it won't run....what seems to be the problem....is it the belt or transmission...let me know pls...ty

Answer
It could possibly be a belt is broke, or something wrong with the
transmission, is it a hydrostat drive?  Can the mower be pushed when not running?  Find the model number on the tag under the seat,
and let me know what it is, and I can give you better advice.

Thanks,
 Fish