Hi I just bought a brand new DN2820 this week.
I plugged it to a 1920x1080 screen via HDMI to HDMI (lets call it setup 1)
I downloaded the latest BIOS : 0.28
Upgraded the bios
Followed instructions to installed ubuntu
I installed ubuntu, it worked fine 
Today plugged the Nuc on another screen that is 1920x1200 via HDMI to DVI (lets call it setup 2)
it worked I could boot to ubuntu and use it.
then I made a reboot "sudo reboot"
I got the message : "signal error" on my screen
I don t see the NUC startup screen at all.
I plugged back the NUC on setup 1 : I have a black screen and still I don't see the "NUC" startup anymore.
What do you suggest ? I read the video support and could not find a solution.