Weird black screen - X41T

[Yotam]

Hi,

It happened twice, so I must know what is it.
Suddenly, while surfing the Internet or doing something else (I don't remember what did I do on the first time it happened but now I was just surfing the Internet), the screen goes black and I can see nothing.
It doesn't turn off. I can still use the brightness keys and I see the backlight changes as I press them but nothing appears on the screen.
I can see the computer is still working. Not sleeping or something. If I press keys it responses and works - but nothing on the screen.
The only solution I found is to sleep it (by Fn+F4 or closing the screen). After it goes to sleep and I wake it up, everything is OK.

Do you guys know something about that?

I hope you understand me and my English.

Yotam