2003 craftsman riding mower 18.5 hp wont start?

Most mowers this size would not have the blade(S) mounted on the engine crankshaft there would be a mower deck and the blade(S) are on spindles .....Assuming the engine is a vertical shaft engine and you hit something and stopped the blade(S) from turning AS in NOW....I suppose it is possible you stripped the woodruff key in the flywheel/shaft at the top of the engine and the engine is out of time....Might need to talk with a Sears repair tech....