If your microphone isn't working, try the following...
1. Go to "Control Panel".
2. Click on "Sound".
3. Click the "Recording" tab.
4. Click on the device you are trying to fix.
5. Now click the "Configure" button and then click "Set up Microphone".
6. Once that is complete, click the "Properties" button.
7. When you are done with your changes, in "Properties", click "Apply" and then "OK".
8. Then click "OK", again, on the main "Sound window".
Now if the device doesn't' show there at all, no matter what you try, then the3.5mm port you are connecting to may actually not work for both input/output, which is what is needed to use a headset/mic combo. It could also be one of the ones I have seen a lot recently that say the are dual (input/output) but then don't really work with headsets.
A way to work around this is to get a USB to 3.5mm adapter and connect the headset through a USB port instead. It would work through that.