DDJ SX

My DDJ SX has always worked perfectly, however I am now having an issue with channels 2 & 4 not having any volume through the Master Channel and the lights on the Master Channel are not lighting up. The individual channels light up and I can hear sound through the headphones whilst cueing on all channels. Channels 1 & 3 are working absolutely fine, I'm really flummoxed, it's like the right hand side has just muted. Played a five hour set on the controller 4 days ago and everything was fine.