What mic? How do you have it defined? i.e. is it defined as an audio source from "sources" or is defined as a source in settings? Also if you open up the sound control panel have you confirmed when talking into the mic that Windows can actually hear the audio (the meter should register)? If nothing is seen in Windows, do you have the freq and bit rate set correctly for the mic within the control panel (advanced tab I think)? What tracks do you have defined in the advanced audio properties of OBS? If the meter in OBS sees the audio but nothing is being recorded then you have a "track" issue.
General tack rule - everything gets track one but each source only gets a unique non-1 track... i.e. desktop audio gets 1 and 2, mic1 gets 1 and 3, mic 2 gets 1 and 4...