You broke a pin in the brown ribbon cable that is at the bottom of the LCD. It's not fixable. This is a fairly common problem when installing a backlight.

Here's the thread:
http://chipmusic.org/forums/topic/11256 … r-dmg-lcd/

What your problem is seems to be the ribbon cable. In order to connect the ribbon the the back PCB you have to bend it and push it in, but after doing that a few times, the metal inside the ribbons can snap and cause it to disconnect. There's no solution other than amputating a cable from another gameboy and resoldering it in. It can be really difficult due to the awkward placement of the ribbon's solder behind the LCD. Ill link you to the thread where I attempted the same thing (I believe luftek did it well!). Bare with me!

.

Thought those were horizontal? ;O

But yes, upload a pic if you can.

.

It might be the ribboncable that attaches to the screen. You may have to heat it up a bunch to make the contacts re-attach.
I know that it's hidden below a small rubber strip on the bottom of the LCD.

I think? :I

Ok, so I have this really cool looking DMG I modded it is fluorescent green with a red backlight, nes buttons and RCA prosound. The problem is very occasionally I have to slightly squeeze the gameboy to get the display to display correctly. It makes this weird  pattern of what look like a lot of vertical lines that go from a very faint grey to some being black. I have taken it apart various times to look for shorts, and found none. It is an LEDx3 Backlight from kitsch wired up to Q1 and the led ground. It has the resister that came with the kit wired as well. I do not have a camera capable of taking pictures that are not super blurry, sorry.