If you are using a MacBook, it may help to hit the Volume up button (F12, located near the top-right corner of the keyboard) a few times. If there’s no microphone in this list, either the device drivers of the microphone have not been installed, or there’s no working microphone present at all. Locating and installing the device drivers may help, but perhaps trying to find a second computer would be a good idea. Another good idea, would be using headphones with a built-in microphone.