Installing the latest windows updates fix previous problems as well, Lets install available windows updates first.
Microsoft regularly releases windows updates with the latest bug fix and security improvements. Press one of them or probably have to hold down the Fn key while using these keys and check if you are able to change the screen brightness. If you’re a laptop user, Look for a sun symbol on your keyboard these keys are function keys on the laptop that used to adjust (Up or down) screen brightness on your laptop. This will restart all drivers including the Graphics driver and fix if a temporary glitch prevents screen brightness function normally. If this is the very first time, you are unable to adjust the display brightness with dedicated keys on your keyboard, or brightness slider we recommend reboot your PC.
