djm 850 soundcard wont connect to my laptop.

ever since yesterday my djm 850 wont connect to my laptop. usually when this happened i could go into system preferences and it would be in the 'sound' and select the device as the output, but this time it is not the case. tested on on different usb cables and laptops and nothing has worked yet. all fingers point to the usb port on the 850 ! anyone else had a problem like this?