Backlit stop working on inspiron 7537

Hi,

after reinstall quickset driver (reinstalled sound driver and maxxaudio disappear, so i reinstall quickset too) i cant enable keyborad backlit on my dell inspirion 7537. Backlight button just doesn't working and bios says keyboard model: None (previously it says Backlit keyboard). I've update bios, but it doesn't done anything. Also, windows mobile center says there is no backlit.

p.s other fn keys works fine.

model: Dell Inspiron 7537 (i5-4200U, without touchscreen)

os: windows 8.1 x64 SL ENG

sry for my english