it can be one of four things that i can think of, the rope is stuck in houseing ,take it off to check its roundabout three bolts, the brake is stuck on (if fitted) check control cable, the piston has a hydraulic lock caused by fuel or oil getting into cyl head (the result of tipping machine on its side to clean it) etc, take out spark plug it will blow out the oil when spun over or the worst case its siezed, lack of oil is mostly the main cause of that
peter bainbridge, October 2006