|Do you really know that the keyboard isn't working?|
If the screen is black, it would be difficult to determine
that there is also a problem with the keyboard.
If it is just the screen, it is most likely a broken ribbon cable
in the hinge. Sometimes you can raise the screen just enough
to turn the laptop on, and the broken cable ends momentarily
touch, so you can tell that that is in fact the problem. The
cable should be fairly easy to replace. You can probably find
a new one for your specific laptop model on the web. I've seen
generic instructions on the web for replacing video ribbon cables.
Or any computer repair shop can replace it for a fee in addition
to the cost of the part.
Other possibilities are that the cable just came loose, or that the
light source died.
-- Jeff, in Minneapolis