OK it's simple but we will repeat it another time: for those who have problem with their LCD display the FIRST step is to connect the computer to an external monitor. Don't buy any part until you can do an accurate diagnostic.
(Most of the times) if you get a normal video signal on the external monitor then your logic board is probably OK.
You have a normal video feed on the external monitor but the internal display is only lightened (grey) or image is distorted then the problem is probably the video LVDS cable (bad connection or faulty) or the LCD panel has a problem. Pixels lines in the display = bad LCD panel.
You have normal video on the external monitor and the internal screen is black but you can see a faint image of the desktop when lightning the rear of the display with a flashlight then the problem could be the inverter cable (faulty or bad connection), the inverter board, the backlight.
Normal video on external monitor but video on internal display is intermittent when moving the display up and down. The display will only work at a certain angle. Most of the time the problem is the reed switch cable, a cable (double wires) that is part of the inverter cable on iBooks G3/G4.
You have no video or distorted video on the external/internal monitors and the computer freeze when booting or when moved then the graphic processor unit (GPU) is probably faulty that means replacing the logic board.