The starter is stuck on the ring gear.A common happening with flathead starters. The engine will be locked up, too. Put the trans in high gear and rock the car back and forth by hand, may take a couple of buddies helping. You'll hear the engine start to turn, or just have the hood open and watch. Be sure the key is OFF! Y-blocks and 223 sixes will do the same thing. If you have one with an automatic, it usually requires starter removal. Sometimes a socket wrench on the crank hub bolt will turn it enough.