Win 10 audio server using USB connection to Stellar Gaincell DAC

I wonder if my Stellar DAC has a problem. First here’s my configuration. I
My server is located in the basement and remotely control it.
Connected to a USB 2 port is a Ulink UL-10 pair, interconnected with a Cat5 dedicated cable.

When I initially set this up, it was working fine… then…

I have gone through all sorts of testing, even replacing the UL-10 pair, but the DAC is no longer found. On the receiver end, I have a zip drive as well as the DAC plugged in. I power everything up and down in various order and the zip drive is found an usable in every time. I have even reinstalled Windows (UGH). Whenever I try to install the PSaudio USB driver I get the following message.
“Setup requires that the device is plugged in. Please connect the device you
want to install and make sure it is turned on. If your device is currently
connected, please unplug and replug it.”

How do I, or have I, determined that the DAC is the problem?

Have determined with PSAudio that the DAC is defective and am returning it for repair.