Internal and External microphone isn't working
I use a MacBook Pro, but I've noticed this behaviour with some software, where the audio gain in System Preferences gets reduced to zero (i.e., no mic input). I suggest the following procedure:


Launch the software that you're having difficuty with.
Go System Preferences >> Sound >> Input
Increase the Input volume slider as desired
Switch back to your software application, without closing the System Preferences dialog.


For some reason, if you close System Preferences, then this can cause the software to reassert zero gain.

You might also want to consider resetting the system, just to ensure that you're resetting anything that might be inadvertently causing your issue.