Lumia 1520 :: Not Recognized On Any Computer

Running the latest DP build of WP 8.1 (8.10.12397.895) and, of course, would like to downgrade back to WP 8 so I can get the Cyan update.

Problem is that my phone is not being recognized on any computer I plug it into.

I've tried two Win 8.1 machines, a Win 2K12 and a Win 7. On all of them, I've completely uninstalled all of the Nokia software (three of the four machines had never had the software installed) and then reinstalled both the NSU and NSU for Retail. No go.

I did a reset on my phone. No go.

I removed both the SIM and the SD card. No go.

I've toggled the hidden USB settings on the phone. No go.

I've rebooted the phone upteen times. No go.

The phone is simply not being detected by the desktop OS and is not being installed on the computer.

I've tried everything I can think of to get this to work.