More often than not, I use the dedicated keys on my ThinkPad to change the screen brightness. At times, I also use the screen brightness slider in the Settings > Display to adjust the screen brightness accurately. Like most others, I also manually reduce the screen brightness at night and increase during the daytime. This morning, while trying to increase the screen brightness using dedicated keys on the keyboard, I could not increase the brightness. The brightness slider in the Settings > Display section was working, but it was not helping to increase the brightness beyond about 40% of the actual screen brightness. If you are also unable to increase the screen brightness on your PC, please try each of the following solutions in order. Solution 1 of 4 Try all four ways to change the screen brightness If you are unable to adjust the display brightness with dedicated keys on your keyboard, please try other methods as well. Refer to our four ways to adjust screen brightness in Windows 10 guide and make sure that the screen brightness is not increasing even after attempting all methods. Solution 2 of 4 Reboot your PC once Rebooting your PC restart all drives, including the graphics driver. Restarting the display driver, at times, resolves display issues. Try to increase the screen brightness now. It might work. Solution 3 of 4 Turn off adaptive brightness On PCs that are equipped with an ambient light sensor (most laptops and tablets have), adaptive screen brightness feature in Windows 10 automatically adjusts the screen brightness to match the ambient light. When this feature is turned on, it doesn’t allow you to manually increase the screen brightness much. Turning it off should allow you to increase the screen brightness. For the record, turning off adaptive screen brightness fixed my issue. Here is how to do that. Step 1: Right-click on the battery icon on the taskbar and then click Power Options to open the same. Step 2: Under Selected plan (power plan), click the Change plan settings link next to the current plan. This will open Edit Plan Settings window. Step 3: Click Change advanced power settings link. Step 4: Expand Display tree, expand Enable adaptive brightness and then turn off the feature for On battery and Plugged in options. Click Apply. You should now be able to increase the screen brightness. Note that you might need to turn off adaptive brightness for other power plans as well if you use more than one power plan. Solution 4 of 4 Reinstall the display driver Reinstalling the display driver is the ultimate solution to screen brightness not working/increasing issue. To reinstall the driver, you need to uninstall the current display drive first and install a fresh copy of the driver. You can refer to our how to reinstall the display driver in Windows 10 article for step-by-step directions. After reinstalling the display driver, be sure to turn off adaptive screen brightness. How to adjust backlit keyboard brightness in Windows 10 article might also interest you.