Remove the spark plug and try again. If it pulls, compare the new plug against the old one. If you installed a plug that was too long, the piston could hit it and keep the crank from rotating. If oil or fuel comes out of the spark plug hole, the engine was "hydrolocked." If it is oil, check to make sure it is not overfilled. If it is fuel, check the oil for fuel contamination, change again if necessary. If all else fail;s, try rotating the crank by hand and not with the recoil starter. The rope can get tangled or debris can bind the pulley.