My problem is that I can't change the brightness level of my laptop screen. I tryed to change it with the Fn key combination of my keyboard, and Ubuntu shows its brightness bar moving up and down, but the screen doesn't change the brightness.

I tryed with some scripts that I found at Google (that's one of that links, but nothing works... Neither xbacklight nor backlight scripts.

Can someone help me with this problem?

(Sorry if there are some mistakes, my English is not very good...)