What would make the horn not work?

If you don't have electrical diagnosis skills, this is going to be tough, but with a test light and a wiring diagram, this is fairly quick to diagnose. There are 2 horns, so it's unlikely they both failed, but one could have failed earlier and you didn't realize it, and the other may have just gone out too, so check for power to both horns when pushing the horn button. Check the horn relay, #40 in the under hood fuse box. If the relay is exactly the same as others in the fuse box, you can try swapping another relay to see if it works, just make sure the part# on the relays are exactly the same!