"the system is running in low graphics mode" I get this message when I boot my ubuntu

It is not related to nvidia drivers. Because by default Ubuntu uses non-nvidia drivers even though you might have nvidia GPUs. I have an nvidia GPU too.

My Ubuntu used to boot fine until something happened which caused the same issue. After reading posts, reading logs and little bit trial and error, turns out the problem is related to lightdm GUI server.

I dont know solution to the problem but there is a quick work around in 3 steps. This will save you from reinstalling Ubuntu.

• Step 1: When the error shows up, hit Ctrl+Alt+F1. This will open the commandline interface. Login as root.

• Step 2: Remove a particular X11 config file. This file is not really required.

  rm /etc/X11/xorg.conf.failsafe
  

  Somehow the existence of the above X11 configuration file causes the OS to throw that error.

• Step 3: Restart lightdm with:

  service lightdm restart
  

  This will restart lightdm and voila your desktop is back!

You can solve this problem by following the instructions here: https://answers.launchpad.net/ubuntu/+source/nvidia-graphics-drivers/+question/218729