Hi there, on your system do you see a DisplayPort and an HDMI out? you should be able to use either connection to extend the desktop. Did you see these outputs on there or already try, just wanted to make sure I didn't miss anything?
The Dell 7450 AIO has a Display port and an HDMI Out port. The system also has a button on the right side of screen just above power on button, when pressed the first time screen displays "PC", pressed again screen displays "HDMI", pressed again screen displays "HDMI ?". The words PC, HDMI and HDMI? will display in the lower right side of screen. However image on desktop never changes and second monitor goes to power saving mode.
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.
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.