Brightness Control Inspiron 3521

Hey,

I have updated my OS to Windows 7 and i am unable to change my screen brightness levels and have the following issues with it

1. The F4 and F5 only decreases brightness levels by one blip/level.So my brightness is almost full all the time.This means that the keys of F4 and F5 are working but not properly
2. The Power tab in control panel shows no brightness level 
3. I tried installed all recommended drivers.
4. This issue doesn't arise if i work in Linux OS

Please suggest a suitable solution