Windows 8 Fn key doesn't work for brightness

Question

I have an Asus laptop with Windows 8 and clicking Fn+F5 / Fn+F6 keys (for brightness) doesn't work. In fact, they work, but they can increase/decrease the brightness only one time. What I mean is that after pressing Fn+F5 once, nothing happens if I try to press Fn+F5 again, before I press Fn+F6.

This only happens after logging in. At the login screen and during Windows boot I can adjust the brightness as I want, but after login I can't.

I installed the latest ATK driver and NVIDIA graphics driver for Windows 8, and I think that my problem is related to conflict with drivers. I tried to reinstall/delete some drivers, but it didn't help.
How can I detect where is the problem?

Solution

If keys works before logon, thought you need to check programs which starts after logon. Disable them one-by-one and logoff/logon?

You may disable startup programs in Task manager on "Start-up" page.

Comments

[Airat Shigapov]

It is Asus K53SJ.

[Erik Funkenbusch]

You could try uninstalling the ATK driver.

[Prerak Diwan]

This is probably a driver issue.

[Airat Shigapov]

Already did. I tried to disable all programms at startup, but it didn't help.

[user1984103]

This might be a driver issue. Make sure you have all the proper drivers for your system's motherboard/chipset installed.