Thank you for taking the time to report this bug and helping to make Ubuntu better. Could you tell us what you computer is? Is this an external monitor used on a laptop? Please try using the safe graphics mode (press F4 in the startup screen) and disable desktop effects via System -> Preferences -> Appearance, clicking on "Visual effects" and choosing "None".
Thank you for taking the time to report this bug and helping to make Ubuntu better. Could you tell us what you computer is? Is this an external monitor used on a laptop? Please try using the safe graphics mode (press F4 in the startup screen) and disable desktop effects via System -> Preferences -> Appearance, clicking on "Visual effects" and choosing "None".