If the motor won't "turn over", remove the spark plugs, and try to turn the motor over with a ratchet and socket. if it still won't turn over , two things to check and they are both bad, first take an led pin light and look into the spark plug hole, see any dents , chunks of aluminum? if so then something in that cylinder may have broken, ring or piston and it will not let the motor turn over because it is hitting the top of the block, nothing there drop the lower unit to make sure that water hasn't rusted and seized the top drive shaft bearing causing the lower unit to not allow the motor to turn over, the drive shaft goes into the crank and if it locks up, starter will not turn over the power head. I would guess lower unit, did the oil get checked, changed prior to running, if there was no oil the bearings will weld them selves to the surface they are touching, I have seen this in motors that sat and then tried to get running, maybe was the lower unit drained and not refilled?