when playing music stops for a second 3 or 4 times in an hour

I tried to download the firmware on my mac book but it keeps reading that my ddj sx is not connected this is an issue i have had from day one i turned off the screen saver and hard drive sleep mode turned off auto gain updated tp 1.1.1. and i cant get away from this problem.I have A mac book os 10.6.8   2ghz  intel core duo 2gb 667 mhz

ddr2 sdram 100gb hard drive  also in the dj mixer tab I cant split the headphone can anybody help me !