Dell Inspiron 8500 screen becomes white

Hello,

I have a Dell Inspiron 8500 (almost 4yrs old) that displays nothing but a white light from the LCD panel. I have pulled the LCD panel and checked the connections (removed/replaced) and they all seem fine. I've connected an external monitor to the laptop and that works fine. Is the problem the panel or the inverter? Is there a way to check or should I go ahead and replace the inverter since that's the least expensive option to start with. I can't see spending $400 dollars to replace the panel. Thanks for any help.