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 they don't show in there, right click on the white background of that window and make sure both "Show disabled devices" and "Show disconnected devices" is checked.
Should none of that work, right click on the speaker icon in the taskbar and then click "Open Volume Mixer". Make sure that the speakers aren't muted there.
If, after all this, they still don't work, then it may well be that the speakers themselves are the problem.