Brightness of Screen

The screen on my laptop randomly decided to go dim on me as I was typing a paper. I have tried using the sun button on the key board to adjust the brightness, but nothing happens. How can I fix this problem so that I can actually see what I am doing on my laptop, even when I am not sitting in front of a window with light streaming in? If anyone out there has a basic knowledge of computers, and can help me, I will be eternally grateful. My cousin's boyfriend tried to help, and he works for a computer company, but he was stumped by this problem.

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