Display continues to darken. Brightness keys do not work.

Display has become fairly dark. This has happened over a couple of months; now too dark to ignore further. Brightness keys have not worked for several months. We can drive a monitor without any problems. This MacBook Pro is fully charged; its power cable is attached and plugged in. This 13-inch unit was purchased in mid-2009 and we are running Mac OS X Lion 10.7.5. We have never had any problems with this laptop. Is this the beginning of the end?