Hi ChrisChambers1988,
Welcome to Microsoft Community. I understand that you're not able to record any narration in Movie Maker. It's possible that the mic you're using is not properly plugged in so to rule out that this is contributing to the issue, kindly plug in and plug out your mic.
Furthermore, kindly record a narration using your computer's Sound Recorder then check if you can hear the audio afterwards.
Let us know how things turn out.
Thank you.