Why won't my screen brightness button work?

I recently dropped my Gameboy Advance SP and afterwards the screen brightness did not work anymore. There are two options when pressing the screen brightness button (the button with the little sun near the hinge) - 1. A darker screen where you can only really see it when held up to light in a certain way, and - 2. A lighter screen where it is easier to see the game clearly. The screen, regardless if I press the brightness button or not, stays on the darker screen (option 1). I'm not sure what to do - whether this is a common occurrence and can be fixed easily at home, or whether I have to see a professional at a Nintendo place (or something like that). Please help!