Hi Metalhead,
sounds like an issue we run into last year while setting up a test system in our labor. In stock we had had an old CRT and connected it to the DVI by using an adapter to VGA with the same result you have. It seemed the video card didn’t activate the port while not “seeing” a monitor is connected. We changed the monitor to a TFT without the adapter and every thing was fine. Maybe using an other adapter from another manufacturer will do the job.
But that’s just a guess and maybe only a little help.
(Edit: spelling)