I have a Dell Inspiron 1720 and wasn’t happy with the brightness, even after pressing Fn up arrow – it would only get so bright. Despite trying everything within Windows to make it brighter, it occurred to me there might be a setting in the BIOS and there is.
On startup, press F2 to enter the BIOS setup and expand the “Video” option. There should be two options beneath that – “Brightness” and “Brightness (AC)”. Select “Brightness” and change the value to 8 instead of 3. It’s brighter on AC b/c the “Brightness (AC)” default is 8 whereas on battery, the default is 3. The value set in the BIOS is the maximum, so you can’t set the brightness beyond whatever is set in the BIOS.
After booting into Windows (or your favorite OS), you can then adjust the brightness as bright as you like.