Tricky laptop repair question. Ideas anyone?

Hi all
Been fixing laptops a while, so know what I’m up to, but…

Have a Dell Insipron 2650. Was dropped (i’m told) by previous owner. Here is the symptom:

On startup, the video image is stretched, off-centre and lined. Basically unviewable, but there is still an output.

So, graphics card problem? No. Displays ok on external monitor and replacement card has same problem.

Here’s the curious thing though - if you power on with the lcd ribbon unplugged THEN plug in a second or so after powering on, the image is perfect and remains so.

So what is the problem here? The screen itself is fine as has been checked. Could this be an lcd ribbon problem? Or is it more likely to be a motherboard issue?

Any thoughts on this one would be interesting and useful, as I’m pretty stumped with it at the moment…

Thanks in advance