Heres something that takes less time to do than tell you how. Loosen starter mounting bolts enough to alow shaking starter side to side a few times then retighten bolts and this time don't be timid when you short accross terminals. Thats to say don't pull screwdriver away at first spark. Report back with results and we can take it from there.
/ Is my starter motor faulty only getting sparks no noise? Hotwiring