Original MacBook Air sound cable
I don't know why it fails, but when you lose the sound card on your First generation MacBook Air, 1.1, 2.1, it is probably this cable. Unplugging and replugging the cable inside doesn't seem to help. This is the second time I have had to replace this cable.
I have had my Air open for a prior cable repair and a hard drive replacement, so I have worked on it before. I had the new part in, and the case screwed shut in about 10 minutes. This did fix my problem (both times).
DON'T LOSE THE SCREWS! They are very small and almost impossible to find if you drop them. I loosened each screw and carefully removed the screwdriver while holding the screw in it's hole. I then carefully pried up the top (the end with the vent holes first, there is a small lip the front slides under) and moved the whole bottom with the screws in place. Do not move it more than arms length, if you drop it you've lost all the screws. Careful is the operative word here.