If connections tight and battery full charged, try taping the starter lightly with hammer while trying to start. Or, if the rear of the starter has a rubber plug or square shaft protruding , take wrench (9/16 or 1/2) and turn starter and try again. If that doesn't work try jumping it. Starter may be stuck on flywheel. You can also put in reverse and try to unjamb starter by rocking car back and forth. Otherwise load test battery and starter,