Dead LVDS cable?

i received a broken MacBook Pro 17". It was dead because of water damage. I ordered a brand new logic board, with the integrated video cards & CPU, installed it properly, and now when i boot my mac the internal display is showing only a blank screen. External video is working fine though, as I am typing on it right now on my external display. My question is, could it be the LCD who suffered that much from the water spill, or do I just need to replace the LVDS cable? I wouldn't like having to order a new display. Sometimes when I switch to the next desktop with Mission Control in OSX Lion, I can see the black vertical line separating 2 desktops move on my internal display, as it would do if the display was working, but it isn't black, it's more like a very light purple tone.

Any help would be much appreciated.

Thanks in advance.