Take the keyboard off and reseat the vidoe card and the cable coming from the card to the screen. Although the cable to the screen wouldn't effect the external monitor so it is probably the video card that has come loose.

Thanks,

I take it that the keyboard is removed by loosening the screws marked 'K' on the underside of the machine?

Jon

Yes and NO. You have to remove all the K screws. Use the "Product Support" button on the top left of this page to download the service manual for your model. It will give you the details of how to remove the keyboard and any other removable part/assembly of you notebook.