The situation is as follows:
After upgrading my graphics card (1080ti) I was missing a compatible cable, DVI-I on my second monitor as it was using VGA. This was ok as my primary monitor was using HDMI and was working fine after driver installs and numerous reboots.
After 4 days my DVI-I cable arrived, plugging this in and booting the machine results in boot failing after grub (this appears on the secondary DVI-I monitor). The ubuntu loading wheel comes on screen for a few cycles at which point both screens go black.
Shutting the machine down and unplugging the DVI-I cable results in the same thing despite being in the exact same configuration before plugging in the HDMI cable.
Using the DVI-I connected screen on its own results in same behaviour.
Using recovery mode to drop into a root shell and deleting /etc/X11/xorg.conf rebooting results in same behaviour on both monitors. Similarly running nvidia-xconfig after deleting /etc/X11/xorg.conf results in same behaviour.
Hardware issues are unlikely as booting into windows with both monitors connected results in standard behaviour.
Not tried with the DVI-I monitor but an ubuntu gnome usb 16.04 works with the HDMI connected monitor.
The nvidia driver is version 384.59.
possibly of note i was using a custom xorg.conf prior to this due to restrictions around my mouse (cyborg rat 7 does not play nice out of box with ubuntu, see https://wiki.archlinux.org/index.php/Mad_Catz_Mouse)