Inspiron 5150 screen goes blank when body touched

Sometimes the screen of my Inspiron 5150 laptop goes blank when I touch the area on either side of the mousepad (but usually the left corner).  Occasionally it will also happen when I adjust my screen or touch the bottom side of computer.  When this occurs, I hear a "click" sound as the screen goes blank.  I use an external USB laser mouse, and when the screen goes blank, the light on the mouse goes out too. The power light stays on and the system light blinks periodically, but it's like it's sleeping.  Nothing I do (move mouse, press keys) can revive it so I have to shut it down and restart.  Somedays it doesn't happen at all, other days it will happen several time, usually right after startup.    I've checked the connectors under the keyboard and see no damage.  The laptop has never been dropped.  Any clues?