Please help

I am just starting out with my ddj 400, and i noticed a big problem. I cannot hear anything coming out of my speakers when the audio output is set to the default one but I can hear through the headphones when I play it through my headphones. And when I set audio output to the name of my speakers, my headphones stop working but the speakers are working again. The speakers are connected directly to the computer and the headphones are plugged into the controller