If your external speakers/headphones aren't working, try the following...
1. Go to "Control Panel".
2. Click on "Sound".
3. Make sure you are on the "Playback" tab.
4. Click on the device you are trying to fix.
5. Now click the "Configure" button and follow the prompts. (Be sure you also click the "Test" button.)
6. Once that is complete, click the "Properties" button.
7. When you are done with your changes, in "Properties", click "Apply" and then "OK".
8. Then click "OK", again, on the main "Sound window".
NOTE: If you don't see the headphones listed, try right clicking on the empty space in that window and make sure that "Show disabled devices" and "Show disconnected devices" are both checked.