Go to the control panel, then to hardware and sound, then sound. You should see something called manage audio devices. Plug in your headphones and see if they show up. If they don't, then either your divers(these things will tell your computer what kind of hardware it has and how to use it) are missing or the the headphone jack itself has failed. Lets say it is in fact your drivers that are missing, then all you need to do is either use windows update(it will detect many of your missing drivers) or go to the manufacturers website and look for them there(usually they will have a tab somewhere on the home page that will say something about support or downloads). And also try different headphones, those could have messed up as well.