Big question!
Yes it could be the transaxle (if you have one) or the gears (if you have any) or maybe the transmission belt has just come off?
Make? Model? Transmission type? What were you doing when it stopped driving?
There is not enough detail in the question to offer a valid answer. If you ask a question with more detail, you stand more chance of receiving a definitive answer.
Admin - www.gardenmachinerypro.co.uk, May 2012