I have a Wacom Cintiq 13HD (the first model, not the Touch) which I use on a 15.4" 2009 MacBook Pro with a 2.66 Ghz Processor & 8GB RAM with an NVIDIA GeForce 9400M 256 MB. I use an off-brand (I think it's off-brand) HDMI adaptor to my MiniDisplay port.
The computer is not recognizing the Cintiq. It was all working fine yesterday, then I shut it down last night. When I started it up this morning, it would not work. No matter how many times I restarted, reinstalled the software, even after a disk permissions verification and repair. IT DOES NOT WORK. Also, when I connect just the HDMIadaptor, the displays panel doesn't show the option to detect displays.
My question is, is it the adaptor or is it my MiniDisplay Port?
I would try using an Apple adapter. Some 3rd party adapters cut corners and don't provide full functionality. It's like the 3rd party lightning cables that will charge your iPhone but won't allow it to sync. It should be easy enough to try out an Apple adapter and see if it fixes things. It's more likely that then the port going bad.