I bought a headset mic from Office Depot to use with Skype. The thing is, the mic won't pick up any sound. It's plugged into the audio in, which is working fine, I tested it with my guitar. Audio comes though the earpiece in the headset perfectly. The mic works, I just used it to record my voice on my dad's old Dell laptop. I get zero signal in the sound window in System Preferences. Why would the mic just not work with OS X?