UltraStudio Express Mac 10.10 & 11 not detected

Sys admin at a post house and I have a few Blackmagic Design Ultrastudio express boxes. I've tried a few different version of Blackmagic Desktop Video, but I can't get the boxes to be detected (thunderbolt). I've tried on a few different macs with yosemite and el capitan. From the software requirements, it *should* work. Any ideas? Much thanks!

What exact models of Mac are they? Some of the earlier ones only had Display-port and not TB sockets.

I also assume you've tried a couple of different TB cables as well

As I extract my coffee cup from the wall where I threw it, it turns out it was the *cable*. Thanks everyone for taking a look!