my leptop function brightness key is not working and i can't incress brightness by power option what i do???

[Khevana]

i pressed function key in lenovo windows 8 brightness decresing and not incresing by control panel how to increse brightness

 

[Kneeko]

http/www.tomshardware.com/answers/id-1970223/screen-brightness-function-keys-working-windows.html