hiii… i am using acer e725, my function key is working but i cant reduce or increase screen brightness, but others are working mute,sounds etc, plzzzz tel is dis a drivers prblm or h/ware prblm, if driver prblm plzz give da driver

Did you try at

Hi and Welcome!

for such advanced functions like screen brightness etc, very often some piece of software is needed. You should be able to find it either on the installation media that came with your computer, or on the support website of the computer manufacturer (which should be in this case).