I have noticed this happens a little more often with this Dell model. Let’s try reseating the LCD cable under the keyboard.

First take out the keyboard:
http://support.dell.com/support/edoc...rd.htm#1084976

To reseat the LCD cable go to this page and fallow instruction #8. Then do the reverse of instruction #8 to reseat it back into place:
http://support.dell.com/support/edoc...ay.htm#1084976

If that worked EXCELENT! If it does not. You have a bad LCD.