It's probably your alarm system that's going off. When the battery died, the car's alarm system assumed that someone is tampering with the battery or had disconnected it in order to break into the car. Here's what you can do hook up the jumper cables. The horn will start to blow. As soon as it does, using the key fob, lock and then unlock the doors or basically whatever you usually do to shut off your alarm. once you've disabled the alarm go ahead and try to start up.