Install Nvidia GPU DriversEdit
Ubuntu doesn't include Nvidia drivers by default because Ubuntu's philosophical approach is to think free without cost.  New users, however tend to prefer immediate functionality. If you have an Nvidia graphics card, you may want to install the Nvidia drivers for it.
How to installEdit
Go to System > Administration > Synaptic Package Manager and look for the nvidia-glx package. Right-click the selection and select “Mark for installation.” You’ll be prompted with a list of dependencies, which you’ll need to approve for the application to work. Click Apply to download and install the app. Then open a new terminal (Applications > Accessories > Terminal) and run this command: sudo nvidia-xconfig –add-argb-glx-visuals; follow the prompts and reboot. 
Install ATI GPU DriversEdit
To install ATI drivers you’ll need to disable the Composite option in your xorg.conf. Open a terminal and type sudo gedit /etc/X11/xorg.conf. In the gedit window, scroll to the section labeled Extensions and change the Option “Composite” line from “Enabled” to “Disabled”. Then in your already opened terminal window, type the following six commands:
sudo apt-get update sudo apt-get install linux-restricted-modules-$(uname –r) sudo apt-get install xorg-driver-fglrx sudo depmod –a sudo aticonfig –initial sudo aticonfig –overlay-type=Xv
A system reboot is required to complete the installation.