Welcome to JUST ANSWER small engines, let me try to help you !! More likely the drive belt is broken or off the drive pulleys.
Check the pulley under the seat and see if the belt is on and tight.
Are you talking about the transaxle and engine pulley? It is loose.
Yes, so the pulley has come off?
In order to replace this belt do I need to remove the mower from the tractor?
http://www.managemylife.com/mmh/lis_pdf/OWNM/L0305061.pdf Here is the owners manual with the steps involved. And yes, the first thing to do is drop the deck.