mce controls the backlight, so unless you tinkered with the /etc/mce/mce.ini file and removed the keypad from modules they wouldn't turn off easily.

Might be a hardware problem, I'll leave noobmonk3y to figure out the code that tests the keypad light.

(Just had an idea, R&D mode activates the backlight from bootup on two sides of the keyboard (to indicate system activity), try to enable R&D mode and see if the backlight goes on, if not, it's a hardware problem. Search for R&D in the wiki)