It is pretty common on laptops that are supposed to have dual input/output jacks. If you have checked in "Control Panel" (instructions below) and are unable to access the microphone there to get it working, the your other option would be to try a 3.5mm to USB adapter and connect via a USB port.
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".
NOTE: If you don't see the microphone listed, right click on the white empty background of that window and make sure both disconnected and disabled are checked.