HElp! Screen won't go bright! Emergency!!


I have just restarted my computer and now the screen brightness is very low - I'm struggling to see what I'm typing here!
This happened before but all I had to do was go into Displays and change the slider. Unfortuntaley it's missing this time and the F1 & F2 keys are doing nothing!
Help! I'm using a Powerbook G4 15" Titanium, Tiger OS, etc. etc.
It's crucial that I fix this problem, I film underwater and edit on my laptop - it's my job and I need my screen!