So your belt & chain ARE moving? If so, then make sure the slip clutch under the cover is turning the shaft in it's center. If this center shaft is turning, then almost certainly is the chain inside the box running down to the tiller tine shaft is either worn & came off the sprockets, or broken. If the belt & outer chain are moving, but the center shaft of the slip clutch isn't, then your slip clutch is in need of repair or adjustment. If the belt is moving, but the outer chain isn't, then it could be gearbox problems, or a simple sheared key on it's shafts.
new buyer being a newb , the belt popped off when I was unloading after I bought it ,I fired it up to show the wife and it didnt go ,(figures right in front of her and right after I get it home)it was late after 12:30 so light was not on my side at the moment