Hi,

 The inputs and outputs of the sounds are managed by your soundcard (or the integrated sound shipset of your mother board).

It depends on your sound card which provides the interface with MMM. First you have to check if Mic input is ON and volume is suffisant through the driver of your sound card by clicking on the small speaker in the task bar of Windows, bottom right.

In MMM when you press the red button "Record", the menu allows you to select the inputs provided by your sound card. Choose the input corresponding to your mic. As you can see, it depends on your soundcard.

Note that the recording time in MMM is determined by the "reading window" of the sound.

Regards