Ubuntu 14.04LTS graphics driver: How do I revert to my former set up when I have no display?

I installed Ubuntu 14.04LTS on my PC which has an Asus P5S800-VM motherboard & a Nvidia 5200? graphics card. The system was running fine until I saw that I was running a freeware driver for the Nvidia card & changed it to the proprietry driver in the update utility. The new driver loaded & everything was OK for about 5 minutes & then a window came up saying that the graphics was running on reduced quality & it asked what to do. I told it to stay as it was & then I lost the display. How do I revert to my former set up when I have no display?

1. Open a text-only virtual console by using the keyboard shortcut Ctrl+Alt+F3.

2. At the login: prompt type your username and press Enter.

3. At the Password: prompt type your user password and press Enter.

4. Now you are logged in to a text-only virtual console, and you can run terminal commands from the console. Remove the proprietary Nvidia driver:

   sudo apt-get purge nvidia*
   

5. To reboot the system from the console run the command: sudo reboot. After you reboot, Ubuntu will revert to using the open source Nouveau display driver. Press the keyboard shortcut Ctrl+Alt+F7 to exit from the virtual console (without rebooting). In Ubuntu 17.10 and later to access the GUI from any virtual console press the keyboard combination Ctrl+Alt+F2.

Ubuntu has a built-in command-line utility, ubuntu-drivers-common, for detecting and installing additional proprietary Ubuntu driver packages and their dependencies. The autoinstall command of ubuntu-drivers installs drivers that are appropriate for automatic installation including their dependencies by running the following command:

sudo ubuntu-drivers autoinstall

Ubuntu also has a built-in Additional Drivers GUI utility that will help you to choose the correct proprietary driver for your graphics card. You can always revert to using the open source graphics driver if the proprietary graphics driver doesn't work.

^{⠀⠀Additional Drivers}