I have 2 thunderbolt displays daisy-chained to my mac pro for the past 9 months. I have my sound output coming out of one of my 2 displays. I'm on El Capitan and recently had my displays freeze after waking them up from a lunch break then the sound didn't work and no longer shows up in the sound prefrences panel. Also, none of the USB ports work on either display. Everything is up to date. I've unplugged the Mac Pro and thunderbolt display and still nothing. Any suggestions?