Small Engines (Lawn Mowers, etc.): Poulan 18.0hp 42 cut/ 6-speed, proper manuals, model numbers

Question
When I put my lawn mower into gear backward or forward, it does not move. What could be the problem?  I have checked the battery, changed the belts, etc.  

Answer
 Hello Candice:

 Can you Send me the Model Numbers Off the OEM Tag, Please. With these Numbers I can Locate the Proper Manuals and Better Assist you. However, are you Sure the Belts are Routed Correctly? Is the Pulley on top of the Transaxle Turning. Have Someone Watch while you Engage and Disengage the Clutch. Thanks.

 Respectfully

 John