So I had this exact problem before, where I couldn't get the audio from my microphone, and the audio from the game to record and save as separate files.
I got a computer a few weeks back, and I've set the sound setting exactly the same as on the laptop.
It's set to save the audio while recording. And the first sound device is set to "default" while the second is disabled. This worked on my laptop, and now when I try it on my PC, I get the video file and the sound file. Both of which have both the game and microphone audio on them.
I need help really quickly.