My secondary screen looks like a TV with a bad signal, the screen is a bit snowy. I don't know how to describe it in my own language, so in English its even harder.
Beside the flickring the screens turns black every x amount of seconds and the screens shows a text 'No signal'. Most of the times when this happen the application that I'm using currently crashes.
This behaviour started today, before today it works all fine. I had never this problems with 11.10.
I have an ATI Radeon HD 5xxx and I'm using 12.04.
It began when I had default drivers installed. But when I installed ATI propariety drivers the problem remains.