I have version 16 installed on a new surfacepro running windows 10 and datacad asks me to activate the software every time I open it. Also, if I have an external monitor connected it apparently sees it as another computer because it fails to activate.
Maybe try Ctrl+Right Clicking on the Datacad icon and pick Run as Administrator and run thru the Activation process and see if that sticks. Not sure what might be happening with the second monitor. I'd see if you can get things fixed up without the second monitor first and then once that's smoothed out then add the second monitor and see if things still work.