Check connnections at horn and fuse for horn maybe something came loose and hopefully nothing has shorted. Or maybe the horn just quit from snow, water, corrosion...thats just seems like the easiest things to check. If u have warranty just take it to the dealer
One possibility apart from the obvious that the horns died was that there may be corrosion on the electrical connectors causing increased resistance and preventing the horns from working. In that case a fix would be to unplug them and try and clean the horn and connector terminals.
If you can hear the relay click when you press the horn, but it doesn't go off, its the horn. The same exact thing happened to mine. Started off intermittently not going off when I locked the car, and after a while it just stopped working all together. The connector on the horn seems prone to corrosion as mine was all oxidized when I changed it. The whole horn assembly is only a $35 part from Ford and it takes two seconds to change. I think it took me longer to get the front belly pan off than it did to change the part. Just make sure that you get a pack of replacement push pins because at least one of them will fall apart when you take said belly pan off.