I just installed an Ubuntu Server and after the server was updated, upgraded and rebooted, I get the error "Cannot display this video mode".
It was kinda funny because the server is headless. The monitor was properly connected. I figured it was a resolution error. A little googling around and I found the solution:
It was good though, that I had configured my IP/network settings, so I had SSH access to the box.
1) Edit grub as follows:
sudo nano /etc/default/grub
remove the "#" in front of the line #GRUB_GFXMODE=640X480
2) do ctrl+x to save and exit,
3) sudo upgrade-grub
My screen came back to life.
Thats all folks