Comment 3 for bug 718711

Resolved!

Amazingly how it worked after I gave terminal the command:

sudo apt-get remove xserver-xorg-video-nouveau

Any idea of why this was happening?

Thank you!

PS:

Verbatim from Synaptic Package Manager re: xserver-xorg-video-nouveau

~~~~~

X.Org X server -- Nouveau display driver (experimental)

This driver for the X.Org X server (see xserver-xorg for a further description)
provides support for NVIDIA Riva, TNT, GeForce, and Quadro cards.

Although the nouveau project aims to provide full 3D support it is not yet
complete, and these packages do not include any 3D support.
Users requiring 3D support should use the non-free "nvidia" driver.

This package is built from the FreeDesktop.org xf86-video-nouveau driver.

Canonical provides critical updates for xserver-xorg-video-nouveau until April 2013.

~~~~~