I have a problem with my Sony Vaio SVS1311F3E/W .
When I log in, after have locked the screen for a long period of time, the screen will be black and I can see only the mouse, so I am obliged to restart my computer, savagely.
Processor : Intel Core i5-3210M.
Graphic card : Intel HD Graphics 4000.
RAM : 4 Go.
OS : Ubuntu 12.04 .