What happened to the backlight and how to fix. Thanks.

Try using the Fn key (usually blue text on that key) in combination with the key that controls the brightness (look at the blue colored icons on the keys).

As an example: http://forsale.globalcommaccess.com/images/ToshibaKeyboardFront.jpg
For that keyboard you would hold down the Fn key on the botton left AND the F7 key.