Here's a way to fix your headphones if they short out if you can't go to the store and get new ones.
First, find where the short is. A short is caused by a break in the wire. Typically, headphones short out where the wire connects to the speakers, or, where the wire connects to the part that plugs into the headphone jack. You can usually test where the short is by wiggling the wire. For example, if sound cuts out when the wire near the headphone jack wiggles, that's where the short is. If you're not sure, you can to check to see if all wires are connected to the speaker part. To check the speaker, open up the plastic casing. For some headphones, this is fairly simple to do. For others, you have to poke around to figure out what comes apart. If a piece of plastic breaks in the process, it's OK. You can glue or tape it back together later if you want. Be careful not to damage the speaker itself within the casing.
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Once you figure out where the short is, you may begin exposing the wire. This is a very careful process. Since I described in the first step how to open up the speakers, I'll tell about how to open up the headphone jack connector. To make things simple, cut the connector from the wire. Now, carefully begin stripping the plastic or rubber away from the connector. To strip, simply take your carpet knife, or other similar object (scissors could work, but it would probably be really hard), and cut the plastic away. Go slow and steady, tearing away the plastic as you go so you can make sure not to cut the wire within. If you do end up cutting the wire, it's OK.
After the metal is exposed, you will see two to three wires. These wires are typically color coded. They are usually yellow, white, and red, but may vary. Take note of where each wire is connected, as you will have to reconnect wires to their appropriate places. Strip the wire you had cut, exposing about 1 centimeter of wire. Do this carefully, as the wires are tiny and can break easily.
Head up your soldering iron. If you don't have a soldering iron, you can tape the wires to where they need to go, but solder is more permanent. After the iron is hot, use a small amount of solder to connect each wire to their spots, making sure to not connect wires in any way. Do this one at a time to make it easier, but you don't have to if you're experienced with a soldering iron. If your solder connects between each wire, you can use your carpet knife to separate it. If there's too much solder, use your iron to move the metal in liquid form.
After everything is connected, use duct tape or something similar (scotch tape doesn't work well) to make a new casing. The point of the case is to prevent the wires from bending and breaking away from the solder. Make your case with this in mind. Make sure that there is no exposed wire.
Now, the most crucial step. Plug in your headphones and see if they work. If they don't, the short could of been elsewhere, or a minor mistake while soldering could of occurred. If they don't work, simply review your work. If you have sound, great job. Depending on how well the wires were soldered and how the casing was made, your headphones should last you a good while.