In the command line, type "sudo apt-get install envy" without quotes.
If that doesn't work, install the program from this link: http://albertomilone.com/nvidia_scripts1.html
After it installs, open the program and select the option to uninstall your nVidia driver. After the driver uninstalls, choose the option to install the nVidia driver. Then reboot and your problem will hopefully be taken care of.
Even if it doesn't help, Envy is still a really useful program to have when you want to update your video drivers.