Display contains horizontal multicolor lines

Hi,

I have a 5/6 year old MacBook.

I've had the problems below for about 1 year, but they've steadily been getting worse to the point where I really need to do something about it!

Here's the problem:

The bottom half of the screen appears to be inverted (as if someone has applied reverse video!) and there is a small (1/2 an inch) horizontal line half way in the reverse video zone with multiple multicolored vertical lines inside it. Inside the small horizontal line, it's a dead zone as the display is shunted down by that amount.

If I move the screen around, or apply pressure in random places on my MacBook, sometimes I can get the reverse video to fix itself (so I'm just left with the horizontal line).

I'm certain it's not my graphics chip as when I connect an external screen, everything looks fine

Any ideas?

Does anyone think it's a cable issue or my screen itself?

Is it worth just taking a look inside to see if anything is loose?

Any help would be much appreciated!

Nick.