I have a Toshiba Satellite A105 s4384 running Ubuntu 13.04 and for some reason I cannot change the brightness.

Neither the function keys (Fn + F6/Fn + F7) nor the settings work, and it is really bothersome, as I would like to occasionally decrease the brightness (long car trips where my battery doesn't last, etc.)

Does anyone have any idea? Judging by the suggested questions this seems to be a rather prevalent issue, but none seem to have an answer! I had a similar problem with 12.04 LTS before I upgraded.