Muting external audio (used as template) to record over

When trying to use a song from either youtube or iTunes as a template to record from, I have this problem where the song records into the mix. What I am trying to do (and have tried all avenues I can think of) is find a way of muting/cancelling the external audio and have only my own vocals (guitar, etc.) make it through; essentially being able to make a duplicate of the original song.

I am using a pre-amp (“ART USB Mix - Three Channel Mic-Inst-Line Mixer - Computer Interface”). I am using Windows 7, and Audacity 1.3.

So I presume that you have a microphone plugged into your ART and you want to record from that?
What settings do you have in the device toolbar?

As it says in the pink panel at the top of this page, Audacity 1.2.x and 1.3.x are obsolete and no longer supported. Please upgrade to the latest 2.1.0 from