I have a late 2007 MBP (A1226 IIRC) running 10.5. The screen's top 1/3 displays correctly, but the bottom 2/3 do not. About two weeks ago, if I slightly bent the screen, applying a bit of force, the display would alter and sometimes become 100% correct. Distortions were common. Now, the top 1/3 is fine and bottom 2/3 is solid black (well, the backlight works for bottom 2/3, but just a nearly-black display).
Thinking it was a bad LVDS cable, I replaced the cable with a new one. The problem persists.
The display is 100% perfect with an external LCD through the DVI port.
What could be the problem? It seems like a cable issue, but I replaced the cable to no avail.
Also, how can I diagnose this? I would try the Apple Hardware Test, but when I put the 10.5 disc into the laptop and reboot, holding down "d" to boot from disc, I can hear the disc spinning up and such, but no matter how long I hold down the "d" key, the second I release the "d" key (even after 2 minutes), 10.5 boots as normal instead of booting from the disc. That being said, the disc is being read perfectly fine.
Oh, one more thing: I use the built-in camera about once every couple weeks, so I can't be sure, but it seems the iSight camera failed the same time the screen did (at the very worst, merely within a week or two of the screen doing the same). It no longer works. When I fire up Photo Booth, the program displays no received signal from the camera.
I had my logic board replaced for free by Apple about 7 or so months ago due to the infamous NVidia issue, and when I went to the Apple Store yesterday, they told me this problem is not the same thing.
That's all I know; I'd be interested in hearing thoughts.
AHT will be of no use at all in diagnosing problems with the LVDS video cable, its connections, or the LCD display itself. If you have replaced the cable and are confident that it's securely connected at both ends, and an external display works properly, then your computer's LCD panel is damaged. Your findings with respect to pressure of various kinds on the display back tend to confirm this diagnosis, because electrical contacts with the panel are made at many points around its edges. When those are disturbed by flexing or racking the panel, contacts can be made and broken improperly, causing all kinds of misbehavior.
For future reference, though it doesn't matter right now: AHT is present only on one of the installer discs that were originally shipped with your computer. No retail OS X installer DVD contains it.