Screen backlight Keys not responding

[Hallivand]

Hey all, I recently acquired a 17" Powerbook G4 1.33Ghz for very cheap. However, the only issue I can see is that while the screen backlight slider moves up and down, the screen itself doesn't dim or become any brighter. Could this be a hardware issue that is fixable or software, as it is running OS X Leopard 10.5.8

Thanks in advance,

 

[Hrududu]

Already tried the PRAM reset?

 

[Hallivand]

I've tried resetting the PRAM, NVRAM and PMU to no avail as well as formatting the OS to clear out any cruft from the previous installation.