1987 Dodge Diplomat car cut off and won't start back up

i got a 1987 dodge diplomat and one day i was cranking my car up and is started up but the i was checking my alternator by taking the positive terminal off the battery to make sure it was charging my battery but whie the positive terminal was still off the battery i got inside the car and hit the gas while still in park and the car cut off and will not start back up i put a new coil on it and still not cranking so i was wondering could you tell me what's wrong with it