I've been out of touch for about a year so I could be way off here but I seem to remember that there was some point on the Mobo where you could check the voltage going to the backlight and it needed to be way higher than the rest of the board...like 30-ish volts? If this rings any bells, check that out. Maybe search about it.
Otherwise, check for shorts and generally just take it apart again and put it back together. Might help...you never know!?
Also, how do you mean exactly that your backlight doesn't work? If it just won't turn on at all, maybe your screen isn't working? If you shine a bright light on the screen can you still see an image?
Anyway, this is pretty much my first post back after a year or so away so any other input would help me as much as you!