Mic not Working with FaceTime on my Mac

When I go into Security and Privacy and click on Microphone, it is not showing anything on the Mac requesting use of the Mic... How to I add it to be able to use FaceTime ? I've searched google a lot and can't find anything that will show me how to add FaceTime or anything really to have access to mic.. Any help would be appreciated... thanks in advance :)

Cobie