Small Engines (Lawn Mowers, etc.): Self Propelled lawn mower, self propelled lawn mower, many different types

Question
We have a Toro GTS 6.75 Self Propelled lawn mower.  However the self propelled function isn't working and the wheels seemed to be locked when trying to roll the mower backward.  What do we need to fix?

Answer
 Hello Joy:

 In Order for me to View a Breakdown of your Drive System on your Mower, I Require the Model Numbers Off of the Frame Please. There are Many Different Types of Transmissions and Drive Systems for the Walk Behind Mowers. Thanks.

 Respectfully

 John