How do I trouble shoot the audio line out? It was working this morning. I got back home and it doesn't work. Headphone output works fine, but I get nothing out of the audio line out. I know the speakers are fine because I'm playing my iPhone through it right now. Really disappointed with the build quality of the Mac Pro. Haven't even had it for a year. First the headphone port flakes out on me (then mysteriously starts working again a few months later. Now the line out port stops working.