I have a late 2010 Mac Pro. The headphone jack used to work fine when I first got it in December of last year. The jack showed up in System Preferences and I was able to switch between my speakers and the headphones easily. I later got a USB headset and haven't used the headphone jack in a few months. Today, my USB headset goes on the fritz and I try to connect headphones to the headphone jack. Unfortunately, they don't show up in System Preferences, so I can't select the headphone output. I reset the computer and it still doesn't show up. I tried Sound Source, but it also doesn't show the headphone port. Please advise.