Also one more thing you can try:
Open your sounds and Audio devices Properties (should be a little speaker on the bottom right of your screen, if not go to the control panel).
Now click on "Advanced" of the first page of the sounds properties
Look at the following speaker settings : Play control and Wave
Under "Play control" and "Wave" are the "Balance" settings right in the middle? It's possible the slider is on the far right. Move it to the middle if it is.