Q: Monitor Connected over Minidisplayport/Thunderbolt not detected

I have a Mid 2012 15inch Macbook Pro retina.

I recently picked up a 24 inch cinema display from a friend and I can't get it to be detected when plugged in to the Minidisplayport/Thunderbolt port.

The monitor is receiving power and has been verified to work (It will even play system sounds if the usb is plugged in on this mac).  My other external monitor works over HDMI.  Other connections connected to either minidisplayport/thunderbolt port work (I have a thunderbolt to ethernet adapter which is allowing me to connect to the internet and send this).

I have tried every trick I have come across.  Sleeping the computer, resetting NVRAM, resetting SCM, trying to detect displays etc.  Could it be a hardware issue with the thunderbolt ports?  Surely they wouldn't work for the ethernet adapter but not work for a monitor?

Any help would be greatly appreciated.