Mid 2009 15" MBP vertical lines - need help troubleshooting

Hi all,

Earlier this month, I bought a 15" Mid-2009 MacBook Pro on Craigslist.

When I checked it out, everything was working fine. The only things I noticed wrong were a slightly lighter spot on the display and that the charger had a fray at the brick.

I couple weeks in, I started having a problem with the display where it would freeze, go "halftone" but still color, and start to fade brighter with vertical lines. Adjusting the tilt angle of the display would correct or cause the problem. I noticed that the black piece on the back of the machine was loose on the left side (facing front of the machine).

I have worked as a computer technician and I also consulted with a friend who is as well. We both determined that it was likely the display cable being compromised in some way, since this only happens when the display is moved.

So, we go to replace the cable. Turns out, it seems this machine has had the cable replaced before, and it was not replaced with an OEM cable. The bezel glass was also not seated correctly and cracked before we even tried to remove it.

After replacing the cable, we had a grey screen with vertical lines, but it soon went away and booted up properly. I packed it up (minus the bezel glass) and brought it home, and ordered replacement glass.

Upon unpacking it at home, the grey vertical lines were back. I zapped the PRAM and it went away. Sortly thereafter, the original symptoms returned. It would gradually fade out with vertical lines. Moving the display corrects or causes the problem. Here is a picture: https://dl.dropbox.com/u/1706335/IMG_0173.jpg

I'm not stumped as to if the problem is that I still have a defective cable, or if there is something wrong with the video card or LCD itself. Has anyone encountered anything like this before?