I had seen that in 16.04 actually, and had to
sudo apt-get purge nvidia*
sudo apt-get install nvidia-somenumber
twice, once to get the thing to at least start to light up the screen when plugged in to Nvidia, second time to get it to let past the login screen. Ctrl+Alt+F2 and plugging monitor into the builtin - not nvidia - is your friend while this bug is hopefully fixed asap!!