I got Toshiba m505 and I can't change the brightness of my screen. I can see the brightness adjusting bar move when I use fn+F6 or fn+F7 keys but nothing happens. I'm using Ubuntu 12.04. I did a lot of search on-line but I can't find anything clear for me to understand.
Sometimes the kernel needs a parameter. Try this:
Open a terminal (Ctrl+Alt+T) and give this command
at the opened window , search for this line
and change it to look exactly like this
proofread , save the document and then
run in terminal this command
Reboot your PC and see if problem solved.