When you go into "Control Panel" and then "Sound". On the "Playback" tab, right click on the white background of that window. Then make sure that both "Show disabled devices" and "Show disconnected devices" are checked.
Then plug in the headphones and see if they show, even as Disconnected or Disabled. If both are checked, but the headphones still aren't working, test them in a different device to make sure it isn't the headphones themselves.
If they work elsewhere, but still not on the laptop, then the 3.5 mm port may be damaged and not working. If the laptop is under warranty, you can contact the manufacturer about having it repaired. If it isn't under warranty, then you can repair it yourself, or take it to someone.
Also, another...