i replaced my horn couple of months ago.
here's the abbreviated troubleshooting process in order of simple to more difficult/time consuming:
1. confirm if the horn relay is clicking when the button is pressed.
2. confirm if fuse is okay.
3. disconnect battery, remove airbag to see if wiring/clock spring are intact (per above post).
4. reconnect battery to test if there is voltage to the horn - you'll have to remove the front bumper cover.
5. if everything checks out, you need to replace your horn.

if you aren't confident you can remove the airbag yourself, take it to a mechanic.