Fn key+arrow issues

Hey. I have a Dell Latitude E6520. I spilled water on it, but it suffered no other apparent issues. 

However, I can't adjust the brightness using the Fn+arrow key shortcut. The Fn key works fine otherwise (such as in PrntScrn) and so do the arrow keys, but the shortcut doesn't work any more.

I can adjust the brightness by battery icon>adjust screen brightness, but I need to adjust the brightness often, so please help.

Thanks.