Black screen

I have a Dell Inspiron 9400 that was working perfectly until I connected a VGA cable from laptop to a flat screen TV. This caused the display panel to go black and unable to boot beyond the windows symbol. Yet all internal diagnostics and Bios indicate that video test passes. External monitor will not display any more than laptop LCD panel. I have been told that if video card on a laptop fails it can not be repaired with out replacing the mother board. Should I try any other tests before I junk this system? Thanks for any help with this matter.