Is the engine seized? Lack of oil would be the reason-if the blades rotate freely then it IS the starter that needs repair. This involves removing the rope when starter is upside down, checking starter spring is not broken. Replace the rope (if necessary) and wind rope loosely. The tension is then obtained by feeding the rope around the pulley,this gets tighter as you do so until rope pulls/retracts
Mowerman
July 2009