Disable stereo mix? mic not working ._.

[Digital Oxide]

I tried to get my buddy on vent, but his mic isn't working.. I disabled "Microphone" under playback, and now he doesn't hear himself in his headphones, which is a good thing.. But I go into recording and "stereo mix" is selected, where microphone should be.

I cannot change this so microphone is selected, the little checkbox just stays ticked under "Stereo mix" anyone know why?