RE: Dell 7450 AIO How to add a second monitor via HDMI out or Disport
Turn out to be a missing video driver (Intel HD Graphics 510 / 530 / 630 Driver) for windows 7. I had a Colleague look at the problem (second set of eye's) and he notice that device manager flagged an unknown device. The unknown device was the video controller.
I'm able to use a second monitor via the display port only. I'll work on the HDMI some other time.
Thanks Brad for your help.