Ug... best not to purchase one of these in the first place. Buy a different card if you can. Nvidia is the worst.
Symptom: Running Ubuntu 16.04 and after loading the proprietary Nvidia driver and rebooting login would fail and loop back to the login screen again.
Removed using the following:
Ctrl+Alt+F1 so you can get to a tty prompt
sudo apt-get remove --purge nvidia*
sudo apt-get install ubuntu-desktop
sudo apt-get autoremove
sudo rm /etc/X11/xorg.conf
echo "nouveau" | sudo tee -a /etc/modules
sudo reboot
sudo apt-get install ubuntu-desktop
sudo apt-get autoremove
sudo rm /etc/X11/xorg.conf
echo "nouveau" | sudo tee -a /etc/modules
sudo reboot
sudo add-apt-repository --remove ppa:graphics-drivers/ppa
sudo apt-get autoremove
sudo apt-get autoclean
sudo apt-get autoremove
sudo apt-get autoclean
+Bryan Payne add me on Google Plus