Cannot change brightness on 8.1

I received an acer Aspire r13 as a school laptop. For some reason I am not able to change the screen brightness. The icon appears like this I have tried using function+arrow keys but nothing works. I have turned off adaptive brightness but still nothing. my laptop is stuck at a very bright level, rendering it unusable during the evening/night. Any help will be much appreciated

Have you checked for newer graphics drivers or graphics control settings program? If you try different drivers and System Restore works on your PC, make a Restore Point before changing the driver so you can get back to square one if things end up being worse.

Another thing you could try is checking out all the settings in the power profiles. Sometimes there is a brightness setting that may override the main setting.

If all else fails there's the old Jedi Support Trick. Boot into Safe Mode and go into Device Manager. Delete or uninstall the offending device and reboot. Windows will say "new hardware found" and install the driver that you deleted. For some weird reason this seems to fix many device issues in Windows. It works quite often and is very low risk.