PROBLEM SOUND CRASHER ON PIONEER MIXER 900 SRT

Today, the music was stopped suddenly when i was playing on stage. Can someone please explain or show me the reason why dis this happen. I would appreciate that :

The computer was connecting via USB port and the CDJ was working normally,after 30-40mins, the sound was stopped, i didnt see audio signal on mixer.2 serato decks on computer and 2 CDJ 2000 Nexus still loading normally

and I still could control it.

Lis of the device and software iam using :

Pionneer Mixer 900 SRT & 2 Decks CDJ 2000 nexus

Macbook Pro MD 313 (MAC OS X Yosemite 10.10.1)

Serato dj 1.7.5

Please help me.Thanks alot