Any advice, or settings somewhere? It is set to auto come on in low light .. and it's not. The brightness up and down keys are working on the display, but not doing anything to the keyboard lighting.
The light sensor seems embedded with the Camera. Try cover the Camera, the keyboard should light immediately.
If you are in a bright environment it will not turn on.
Try taking it into a dark room (pitch black) and press the keyboard brightness key to see if it works. If it doesn't, return it.