If your microphone isn't working, try the following...
- Go to "Control Panel".
- Click on "Sound".
- Click the "Recording" tab.
- Click on the device you are trying to fix.
- Now click the "Configure" button and then click "Set up Microphone".
- Once that is complete, click the "Properties" button.
- When you are done with your changes, in "Properties", click "Apply" and then "OK".
- Then click "OK", again, on the main "Sound window".
Now, it is completely possible that your 3.5 mm port is not input/output, which is what it would need to be to use both a mic and headphones. Or it could be one of the bad ones (some laptops have them) that just don't really work with combo (headphone/mic) and only with individual mic or headphone.
The only way around that, if the port is actually the problem, is to either get the port replaced or get yourself a 3.5mm to USB adapter and connect through a USB port.