If your car worked before then changing the battery shouldn't have affected the key coding. When you say it will not start, does the engine turn over? If it does, then the battery is doing its job. The next thing is to check if the spark plugs are sparking and go on from there. If the engine won't turn over, then the battery is either faulty, not charged or installed improperly. Make sure the cable from the negative terminal is connected to the car body to earth it, and that the connexions to the terminals are good and tight.