In control panel, under sounds and audio devices...
Under the first page titled volume tab through until you hear a button called advanced, then tab on twice more and you should hear another button called advanced. The first opens the volume settings box, but the second is the one you want with options to tell windows what type of speakers/headphones you have. If this is set to stereo then your problem is probably something else that I'm not aware of, sorry.
Hope that helps some.
cx2
-----
To live by honour and to honour life, these are our greatest strengths and our best hopes.