RE: Dell 7450 AIO How to add a second monitor via HDMI out or Disport
What input is your monitor using? And when you have the monitor attached to one of the outputs, can you go into the display/resolution and try to scan for monitors attached? Before monitor goes to sleep etc. I will also try to see if I can find something more on this, but from what I have heard/read on in the past the system should be able to drive both the integrated and an external display w/o issue.
Let me know if anything has changed.