I, too, am aware that this is an old thread but having searched for all sorts of things this thread comes up every time. I DID (eventually) find a solution that works for me. What I had to do was in the Realtek HD Audio Manager- I set the recording volume all the way to the left. Screenshot:
Suddenly my computer is able to magically pick up my microphone with perfect clarity and volume.
I'm also aware that this is kind of a dumb fix. But it works for me on my desktop AND on my laptop (Which had the same issue)