I cannot adjust the brightness on my Acer 5420-5687 laptop. The laptop had frozen so I unplugged it and took out the battery which reset the brightness. I tried using Fn key and holding the either sun key, but that is not working. I really need help with this I cannot use such a bright screen it gives me headaches.

I'm sorry my friend but seems your LCD monitor having problem. There are three options with your LCD monitor. Option 1: repair your LCD monitor *commonly problems are the LCD inverter*. Option 2: Replace LCD monitor with a new LCD monitor. Option 3: Instead using your dim LCD monitor plug CRT or LCD monitor external serve as your monitor. Have a nice day.