im not sure sorry. have you checked: 'start/control panel/sounds and audio devices/volume'
click the 'advanced' tab under 'speaker settings' and set the speaker type to match the kind you have ie/ desktop stereo speakers or 5.1 speakers etc. click apply and then ok.
click the advanced tab under 'device volume' and play with the sliders here while you are playing music etc. to test how it affects the sound. mute anything like 'mic' or 'midi' if you dont use a mic or have a musical instrument attached to the midi port.
you may have a 3d effects slider or similar try lowering or muting this maybe.