Instalation through PPAm just purge your previus install and reinstall again
sudo add-apt-repository ppa:nvidia-vdpau/ppa
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys CEC06767
sudo apt-get update
sudo apt-get install nvidia
If that doesn't work you can try the propietary drivers from Nvidia, you can try this:
Go to http://nvidia.com and download the driver to a known directory (
~/Downloads, for example)
Press Ctrl+Alt+F6 to switch to another Virtual Terminal and login with your User/Password
sudo service lightdm stop (or Nvidia installer will not run, because there's an active X session)
cd ~/Downloads && sudo chmod +x ~/Downloads/NVIDIA-Linux-x86_64-295.33.run (if that's the version you have downloaded, to make the installer executable)
sudo ./NVIDIA-Linux-x86_64-295.33.run and press "OK" to all installer questions (default options)
As the installer finishes, run
sudo reboot now to reboot the machine.
At lightdm, login to Unity 3D and verify if there was any change or improvement.
Make sure you are not running nouveau. You can check if nouveau is loaded by running
lsmod | grep -i nouveau. It should display no results.
Make sure your currently loaded NVidia kernel module is the same version as the installed drivers.
You can check that Nvidia Kernel module is is loaded with
lsmod | grep -i nv. If you installed Nvidia drivers from the proprietary/binary installer from NVidia website/FTP it should output "nvidia".
If you have NVidia installed from Ubuntu repos (pakage
nvidia-current) it should output nvidiafb.
To check the Kernel module version, use
modinfo nvidia or
modinfo nvidiafb. It should output "version: along with other module details.
This version should match the drivers you installed.