Welcome to the forums.
What are you trying to listen to? If it's a media player for example BSplayer, the equalizer might have gotten messed up. Go into options of any player and reset all to default and tell us if that helped.
To rule out that the headphones just "died" on you, or that the headset jack is worn or broken, try with another headset on your computer and also try yours on a different computer. (You'll have to borrow one I guess. If you have iphone ear-sets, they should work too).
Does this happen when you plug the headphones in the front and back? (Try both and tell us).
Some other things to try:
1. Go to the computer manufacturer site and download and re-install the high def audio drivers. (I know it's only a headset issue but try it).