Tape the mic a few times with a pencil - can you hear that.
Right click the small speaker icon (probably lower right screen corner).
Try the troubleshooter to see if that can find or fix anything.
Then select "Recording Devices". Find the mic (should be the default) and start checking through all of the various tabs and properties buttons.
Lots of settings and configuration options. Could be that some other app has pre-empted the headset mic.
Try other microphone(s) in any manner that you can. Objective is prove that all audio ports, cards, etc. do indeed work one way or another.
Hopefully narrowing the problem down to just the headset mic or something else.