I have an MTD rideon mower that has sat for about a year and a half I have replaced the battery, selonoid and starter. After relacing battery it crank once and now won't do anything and the crankshaft is really tight is there anything I can do to get th crankshaft to loosen up

Hi,
Could be the starter pinion wedged in the ring gear. Try manually spinning engine counter-clockwise to counteract, if this is the case.
Could be that after sitting so long that the cylinder filled with fuel and is hydraulically locking. Remove spark plug and try to turn it over to clear the fuel from the cylinder (this should be done carefully as it presents a fire hazard.
Peace,
Clarke