Broken headset

sometimes if you hit hardly the side of the headset that doesen't work , it will work again ( but sometime it will broke it )

throw it out?

i had a problem with my mobo where it would only output to one channel

Sounds like one of the connections are lose or you've split some of the copper. You could either crack it open or look at the wire to see if there's any cuts or bends.
If it's a cut it's generally hard to repair and if you manage it there's often some quality lose. If it's a connection problem you might be able to jerry-rig it back together. Don't expect miracles though.

Try to contact the manufacturer...when they was expensive maybe you get a new pair...when not, try this guide:

link

Or just google "headset [put here the name] only one side works fix" or something like that...

Probably just a broken wire or connection, it could be pretty easy to repair but if you couldn't think of this yourself then it's probably out of your league. :P

You'll have to find the break, strip the wire and re-attach or solder it.

happened to me too, probably something wrong with the wire for the headphone for the other ear try moving it around