Dell 1557 Brightness can't change

I got my Dell 1557 about a month ago and for a while, it seemed just fine with my display brightness. I could change it to however bright I want it to be. Then today, when I turned on my computer, my settings for my display brightness was at the highest when it normally is in the middle. At first I thought nothing of it because I could easily change it with the F4 and F5 buttons, but after I logged on and tried to change it, nothing happened. Not even after I restarted the computer or reinstall the ATI Catalyst Center. Even when I don't have the charger plugged in, it won't let me change it. The buttons themselves work because when I do change the settings, the indicator with the brightness level moves up and down, but the screen doesn't actually get brighter or darker. If someone could help me fix this problem, I would greatly appreciate it.


Specs

Windows 7 Home Premium 64 bit

Core i7-720QM

4GB DDR3 1333Mhz RAM

Full HD 1080p High Brightness LED

 

That happened to me before and I was able to figure out the cause and fix it - all my suggestions are in this thread -

"Dell Studio 1745 - Can't Adjust Brightness"
http://forum.notebookreview.com/showthread.php?t=437213

 

Thank you very much ^^