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 option, if you don't want to get it repaired that is, you could purchase a 3.5mm to USB adapter (one with a single 3.5mm hole, not the dual kind) and connect the headphones through the USB port. Or you could purchase a set of headphones that have a USB on them already.