If your external speakers/headphones aren't working correctly, try the following...
- Go to "Control Panel".
- Click on "Sound".
- Make sure you are on the "Playback" tab.
- Click on the device you are trying to fix.
- Now click the "Configure" button and follow the prompts. (Be sure you also click the "Test" button.)
- Once that is complete, click the "Properties" button.
- When you are done with your changes, in "Properties", click "Apply" and then "OK".
- Then click "OK", again, on the main "Sound window".
You may need to adjust it as the balance could be off.
Should that not fix it, or the balance say it is fine, then the 3.5mm port could be the issue. If that is the case the only way to resolve it is to either have the port replaced or get a 3.5mm to USB adapter and connect through a USB port instead.