When you arrive at the login screen press the keys Ctrl+Alt+F1 to switch to TTY1, there you will be able to login and remove the Nvidia drivers.
I have to also say this problem comes because you have a multiple monitor setup and you can still use gnome-shell by removing the file /etc/X11/xorg.conf (sudo rm /etc/X11/xorg.conf), running nvidia-xconfig (sudo nvidia-xconfig) and rebooting will make your system boot and gnome-shell will work with 1 screen enabled.
Start by following the steps to boot up with 1 monitor only and once in gnome-shell you can think about what to do next (try a new xorg.conf setup or remove the drivers your installed).
Follow these steps:
- Switch to TTY1
Ctrl+Alt+F1
- Make a backup of your
xorg.conf file with a different name
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.backup
- Let Nvidia create a new
xorg.conf file
sudo nvidia-xconfig
- Reboot
sudo reboot
You should boot and be able to run gnome-shell now.