The piston will probably be seized in the barrel,take the spark plug out and spray in a little WD40 put it in second or third gear and push it until the engine is free,when it frees itself make sure it freewheels ok with the clutch lever in as the clutch plates may well be stuck together as well.With a fully charged battery check for a spark,refit and have a go,you might have to bump start it(push start)
Rich, March 2008