No sound comes out when I am using my iPhone alone or when the DDJ-200 is connected.

Check the followings:
　-Check the iPhone audio volume settings. Isn't the Mute turned on?
　-Check the Trim.
　-Aren't all the EQ knobs turned fully to the left?
　-Isn't the Play/Pause button tapped to Pause?
　-Isn't the Tempo -100%?