In Device Manager what do you have showing? Example image below.
In the Control Panel under Sound what is showing for Sound>Recording? If your Microphone is showing, is it set as your default device? If you test the Microphone by speaking, do the bars on the right-side show that it is working?
When was the last time the Microphone worked? Have you checked the User Manual for your computer? What is the make and model of your computer?