Is your starter engaging or is it just not working at all? Do you get a clunk when the starter begins to engage, or when you kick start it? If so then you may need to lay it over and pull off the flywheel cover and look to see if the bolts between the flywheel and the case are backed out. You can only see the ends of them as they screw in from the backside. They should all look the same in comparison with the surface of the flywheel. If they are backing out and slightly engaging the case then the starter will not have enough torque to rotate the engine. A 150lb plus person jumping on a 14 inch lever (the kick starter)will be able to crank the engine, but at some point the problem will become bad enough to lock things up.