Changed ignition car starts and dies didn't before

The Immobilizer is activated because the Key is not recognized and there should be a flashing light on the dash. It depends on what part you replaced. If you only changed the electrical portion of the switch then the Immobilizer will not be activated and the enigine should run. If you changed the lock cylinder and key then that is the cause and will activate the Immobilizer. If you are using the same key then you need to check the antenna ring around the lock cylinder for damage. Each key has a transponder in it and that transponder is programmed to the car. It is possible that the car just does not recognize that key so try another key for that car if you have one. If the car runs with the other key then you need to have the bad key reprogrammed at the Dealer. If you did change the lock cylinder and are trying to use the key that fits that lock then you need to hold the old key next to the antenna ring so it will recognize that key and then the engine should stay running.