Could be it just needs a level / gain adjustment, double check the realtek manager and make sure it detects the device plugged into the jack (otherwise they are dimmed out), and when you plug / unplug it should pop up a box to ask what was plugged in (if autodetection is enabled). If it does not you will have to test it do double check if it is working. If it shows up, you will see the mic icon and there should be some options (mine has "noise supression" for background cancellation and "acoustic echo cancellation" to prevent speaker feedback).
To adjust the gain / boost, right-click the windows speaker icon and select "recording devices". In the "recording" tab, select the "Microphone" and hit "properties". There should be a...