I would suspect you have a loose or bad ground connection.
Need more info like the year, make and model.
You probably have a short in your electrical system. Also the fuse may be burnt out on the horn.
Electrical problem, Bad button/horn.
This problem may be a bad fuse, or a bad control module. It could also be the result of an electrical short or worn wiring insulation in the circuit.
If you are repairing the horn, you will find the horn housing under the front left fender on the "Driver" side of the car near the blinker. You have to get on the ground to see it.
Horn is located on passenger side front of the tire and just behind blinker light. It is attached to the frame work and if you look up under, you will see the square of the horn pointed down.
An electrical problem.
i had the same problem with my truck, electrical problems are the usual thing you should expect, you may want to check the battery first then the rest of the wiring, usually there is a wire on the passenger's side of the radio that comes out a little causing a short, that maybe the problem with your electrical components, if your truck doesn't start, try getting some electrical wiring via a cable and touch the wire to the + side of your battery and to your starter, be careful, there will be a big spark, but if it sparks so much that it burns you, try another spot.
Up underneath the dash on the driver's side are the relays for the door lock, wipers, headlamp, horn and flashers. They are together in a single cluster.
I hope you checked the fuses first.
a dead battery
You might need to refill your blinker fluid. If that does not work, check above the passengers visor..
That depends entirely on what's wrong with the horn. It could be a problem with the horn relay, in which case you simply replace the relay. (Under the hood, in the fuse/relay box next to the battery) It could be a problem with the horn itself, in which case you simply replace the horn. It could be a problem with the horn switch, which is a part of the steering wheel. If that's the case you'll need to replace the steering wheel or horn switch. It could be a problem with the horn wiring, in which case you'll need to track down the specific problem and repair it. Good luck.