paulagarey, The belt may have fell off or may have broke, engagement lever may be loose or tensioner pulley may have fallen off/loose, gear damage in gear box, wheel gear teeth or drive gear damaged/worn, loose/bad input shaft,cable stretched/broke/disengaged. Some of these mower's carried a 4 year warranty I believe, perhaps see if yours is still warrantied and have repaired under warranty if it is. See links below for checking/diagnosing self propelled mowers. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.

https://www.youtube.com/watch?v=3G0a11Vt...

https://www.youtube.com/watch?v=y3ej_jG6...

https://www.youtube.com/watch?v=eSaNVZaU...

https://www.youtube.com/watch?v=_sWrC7Pb...

https://www.youtube.com/watch?v=cqmaQ7Lx...