This is a common problem with that nouveau driver that is still relevant as of three days ago. I got bricked by a kernel update, had to switch to the nouveau driver and my pet supercomputer basically became unusable with all these exact symptoms, to the letter.
If you still haven't solved this problem, please try this once you get yourself into the text mode with one of those magic key combinations:
first check your kernel version:
then attempt to install a package
linux-headers that matches your kernel version. It may say that you're already up to date, which is good. If it tries to install, then good, let it. Something like this:
sudo apt-get install linux-headers-<your kernel version from uname>
After that, install the NVIDIA drivers:
sudo add-apt-repository ppa:graphics-drivers/ppa
sudo apt-get update
sudo apt-get install nvidia-396
The latest version that I use is
396. I'm on
4.13.0-39 kernel. Your version might be different depending on what you're using.
Hope this helps.