Wacom Cintiq pro 13 - aaargh - help

[Prokupatuscrakedatus]

Perhaps one of you can help. DD bought it after testing its features in the shop. Now we tried to set it up.
At the moment the thing works only as a clorified touchpad - the display stays dark / gets no signal.

• the quick install guide consists of a couple of little pictures
• no handbook or users guide everything is online
• the online information seems to leave out great chunks of stuff
• there is one cable amongst the 4 that is not connectable to anything
• We tried it with Windows 7 (Notebook and PC) and Windows 10
• I tried telling my PC to recognize a second display but it doesn't recognize this device.

She is so disappointed, she thinks of taking it back to the shop.

That's a serous piece of professional equipment, how old is your DD?

I use mine with photoshop and indesign, what was she wanting to use it with?

Just had a look, mines is linked via a Wacom link adapter?

Yes it is (I personally have no idea what to do with it) - her problem is not the use of the device as such but the set up.
That is, the display on the cintiq gets no signal. And neither the website, the faqs, or youtube offer a precise answer (Wacom link adapter was not even ben mentioned anywhere)...
I tend to think (after watching a Dutch video) that she needs a different cable or an adapter to tell the PC that there is a second display?