It has a drive shaft on the frame aft of the engine going under a plastic cover.. I have seen these fail often ( they eat a lot of dirt in the u-joint). If it is not the drive shaft, it iis the ratchets behind the drive wheels.. (it will not move if both are failed, it will pull to one side if only one is bad)
Cut and paste this link to see a page that has break downs..
http://www.planopower.com/store/honda/hr215hma.shtml
--Good Luck
Friiy