If all else fails, I can suggest installing the latest <a href="http://www.nvidia.com/object/unix.html">nVidia drivers from the official site</a>, this involves stopping the GDM service, and running the install from a text console. It's recommended to remove existing nvidia packages first, and read the README documentation that comes on the driver page too. It's a good idea to backup before, too. Download the setup and make the file executable. Remember where you saved it. switch to a text console with Ctrl+Alt+F1, and log in. The setup must be run as root, do this with sudo -s to work as root, (*please be careful because as root, you can delete system files, just do root tasks and exit out*). Stop the GDM service with /etc/init.d/gdm stop. Now you can run the nVidia setup with sh NVIDIA-xxx.run. When the setup is done, restart your PC with reboot.