If it's not showing up in Audio MIDI Setup (In Applications>Utilities) then the computer hasn't detected it. I often find that I have to re-boot the computer to get it to recognise that the 8 is plugged into the USB bus - but only when I'm powering the 8 from the USB bus. The Oxygen 8 is a bit sensitive to power source. You may find you want to power it separately, by batteries or through an adaptor. Cheers, Stephen.