Problem with my screen

[Alb_Erc]

I've installed the last one version of Ubuntu (12.04) and I have a problem with my screen. When I'm using the SO, the display shuts off and shuts on periodically. I don't know why buy I want to fix it because it very ackward to work with that, but I don't want to change my SO again :(

Please, help me.

(Sorry, my English isn't very good)