Why is my Compaq Laptop CQ58 screen brightness changer not working?

One day i opened my laptop from sleep and the screen was really dark so I tried to making the display lighter but it was on max so I tried turning it on and off again but still didn't work. Some things I have done before I turned it on was leaving the plug in all night while in sleep mode and i usually close the lid fast. Could this have cause it? How can i fix this? I can't get any external monitor so don't tell me to plug it to any other monitor. I tried pressing F2 and F3 as well.