Question RE: Mac does not detect Ayre QB-9 DAC

I returned from vacation and powered on my audio system. It seems my MAC computer is not detecting my Ayre QB-9 DAC. I go into system preferences, select sound and the Ayre QB-9 is not listed as an output. I called my dealer and they are checking but no answers yet.

I removed and reconnected the USB cable and still no QB-9. Everything worked pefectly before I powered down. A few software upgrades were made but nothing looked strange. I re-booted the MAC several times but the QB-9 is not in the list. It seems the MAC is not seeing the QB-9.

Someone at the store suggested maybe my USB cable has failed. Any suggestions?
Try a different usb port. You can also try plugging it into a different computer just to see if it tries to connect.
Same thing happened to my Macintosh C48 but everything was back to normal after I unplugged the C48 and waited 60 seconds to power it back on.
My dealer connected my Ayre QB-9 DSD DAC to their MAC computer and it also failed to detect the QB-9 DAC (using a different USB cable). This is an exact duplication of the problem I had using my MAC Computer. We checked the fuses and they were okay. The unit is being returned to Ayre for repair. They loaned me a Musical Fidelity M1 DAC. Estimated down time is TBD.

As suggested, we tried a different usb port and also plugged it into a different computer. And, we also checked the Audio MIDI setup. The QB-9 failed to operate in all cases. Thanks again for the suggestions.