My 1997 dodge stratus starts and shuts down after a couple seconds

First of all, the main problem on the car was that the RPM gauge doesn't work then my dad had an idea ."Hey maybe is the BCM lets replace it ". Next day he brings one BCM from another car and replaced the original. Now the car Starts and after couple seconds it shuts off .We installed the old one back and still doing the same i think this could be the anti theft system because now i cant even lock the doors by the switch.I need to know if its the anti theft system how to reset it or Bypass it.