hp - Bottom third of laptop display showing up (sometimes) - How to diagnose?

I took this laptop in on partial-trade for one I had for sale:

http://imgur.com/r7ADFwY,RPzYhh0#1 (Use previous and next buttons to see both pictures)

It's an HP 2000-2A09CA.

EDIT: The few times the bottom third works, it displays what would be the top third of the screen... does this mean anything?

Depending on how the screen is tilted, I can sometimes get the third part to appear. I eliminated the motherboard as a culprit since when it's connected to a TV, it appears fine.

So how do I isolate what specific hardware of the screen is bad? If it's just the adapter, how can I tell? Is there a process of eliminating pieces of hardware that could be the problem? (Similar to how we would remove the hard drive, RAM, etc if a computer doesn't POST)

I have another very similar HP laptop with a smashed screen that's the same size (that somehow still works). How interchangeable are the parts between this generation of HP laptops? I don't have the other laptop near me, but generally speaking in most scenarios, is it similar? I would imagine since HP is fairly low-end, they'd try to make use of similar parts between models to save money.

UPDATE: (Please tell me this is a plausible approach) Today I'm disconnecting the LCD screen from the laptop, and connecting a broken one (that still works and displays). Both are LED and 15.6" and share the same video connection.

In theory, if the exact same thing appears on this other screen. This means it's the video cable.

If it displays correctly, then I need a new LCD.

Would this be a good way to diagnose?

My approach I outlined in my question worked, I attached a different display to the laptop and it displayed fine. Pays to have extra parts kicking around :)

So in my scenario, the LCD screen malfunctioned. I purchased a new LCD screen this weekend and now it works.

So to answer my own question...

So how do I isolate what specific hardware of the screen is bad?

You really can't pinpoint it for certain, having spare parts really helps here, but for the most part, if you don't have any spare parts, these steps will work. These pertain to the LCD screen itself, not the backlight.

1) Connect to external monitor. If problem persists, it's likely video card related.

2) Check video cable connection, on the mother board itself, and the back of the LCD. Make sure it's nice and snug. Try jiggling the cable around, if the image changes, good chance it's the video cable.

3) If the display on an external monitor is fine, and jiggling (or swapping) the video cable doesn't do anything, the LCD screen is likely the culprit.

Swapping parts is the easiest way to tell.

If anyone would like to add to my answer, feel free to comment and I'll add it in.