Mac Pro 5.1 late 2012 stopped working with cinema screen.

your Mac Pro 2012 does not have Thunderbolt-2 ports, or USB-C,

Cinema display LED 27-in A1316 from 2011 is a 2560 by 1440 display that features lead-in cord with three connectors -- Mini DisplayPort, MagSafe-2 and a USB-A pigtail. It does NOT work with the Thunderbolt adapter, but works fine with a USB-C to miniDisplayPort adapter.

It includes three USB 2.0 ports and a convenient single cable with THREE connectors (Mini DisplayPort, MagSafe-2, and USB 2.0), a built-in iSight camera with a mic and a 2.1 speaker system.

This display works great with a USB-C to MINI-DisplayPort adapter.

For use with older Macs like your Mac Pro 2012, you might be using no adapter, or a DisplayPort to Mini DisplayPort adapter. (depending on what card you are using.)

from:

https://everymac.com/monitors/apple/studio_cinema/specs/apple-led-cinema-display-27-inch-specs.html

That's the case I described above.

The Mac 5770 has two Mini DisplayPorts.

Before you pull everything apart to connect to a MacBook Pro, try the other mini DisplayPort. I have seen one port on a graphics card fail and the others continue to work.

ljmm1968 wrote:

well I've just had a bit of time to play around and its my cinema screen that is no-more. I have attached an old borrowed Acer monitor via dvi-D and that worked. i'll now swap out the graphics card for the newer metal capable one i have too see if i can update to a newer iOS than high sierra.

Which exact Cinema display do you have?

Can you provide a picture if you cannot provide a model?

The reason I'm asking, there was an older Apple display where the power brick had an issue, but there was a work around if that was the case.

I see that there are several others that might be called cinema display, including the 30-in Cinema Display that I use. these would use different connection methods.

¿Which is your display?

what graphics card are you running?

Most (but not all) graphics card that are metal-capable will work under High Sierra. Post your card model and readers can look up whether Drivers are already included, and at what point they were introduced.

Proceed slowly, ONE upgrade at a time, so that you can don't get stuck if everything stops working after four upgrades at the same time.