1 more thing to try, right click on your speaker icon on the task bar. Then click on playback devices. Then right click on the device you are using for playback. Select properties, then select levels. On the main speaker level, you should see an icon that says balance, click it. First ensure that both the left and right channels are at the same level. If they are, move the slider to the left and then back to the right on both speakers.
Report back with results.