Solution 1:

  1. Add the Official Graphic Cards PPA

     sudo add-apt-repository ppa:graphics-drivers/ppa
     sudo apt-get update
    
  2. Check which Nvidia Driver Version is the latest: Go to https://www.geforce.com/drivers and pick your GPU, check which one is the non-beta. Today the version is 390.

  3. Leave the X server: Press Ctrl+Alt+F1 it should give you a black screen asking you to log in. After logging in, shut down the x-server with

     sudo service lightdm stop
    
  4. Install your Nvidia Driver

     sudo apt-get install nvidia-driver-390
    
  5. Reboot your PC

     sudo reboot