Sounds like the port is output only. It happens. First test the microphone in another device and make sure it works. If it is fine, then check the port to see if it is only output or if it is supposed to be input/output. If it is the former, then the mic won't work. If it is the latter, then you can 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".
If that doesn't resolve it, then you may need a 3.5mm to USB adapter and connect through that.