Assuming that the replacement screen and ALL connections are correct to that particular unit then the assumption would be that it is a motherboard issue related to onboard video.
The LCD screen on my Dell latitude D630 had vertical lines of many colors and a few black blotches. I was able to see only a few words on the left side of the screen behind the vertical lines. I attached an external monitor and everything worked fine while on external monitor.
Thinking I had a bad LCD screen...I replaced the LCD screen with a new one that came with a new inverter. Then I only got backlighting showing on the screen. I tried another NEW LCD screen, replaced the LCD cable with new one and still have the same problem..only see backlighting. If I attach to an external monitor then everything is fine while on external monitor. Please help me trouble shoot this farther. Where do I go from here?