I have a Dell Inspiron 5520 with intel core i7 and AMD Graphics card. It used to work fine with Ubuntu 12.04 and Ubuntu 12.10. Now I tried to install Ubuntu 13.04 but i can't change display brightness: the FN keys don't change it, the indicator shows it always almost full, but won't change, won't increase or decrease. The same problem is there for both x86 and amd64 versions of Ubuntu.
What's the problem?