Yeah, alas it still could be the kind that although are supposed to work with both, don't always.
Something else you could try, when it is connected. Go into "Control Panel", then "Sounds". Click on the "Recording" tab. Now right click on the background of that window (not on any items) and make sure it is set to show you and disabled or disconnected items. If the mic is somehow disabled this will then allow you access to it so you can turn this option on.
How if that doesn't do it, on that same screen, highlight the microphone that is listed (probably the computers mic). Once it is highlighted, right click on it and click "Disable". Then try and see if the headset one will work.