Macbook Pro 2.4 video problem

Hey, My macbook pro 2.4 is having video problems. For the past month the lcd on the macbook pro seems to work sometime and doesn't sometimes. Whenever I plug it into an external monitor it works everytime. What could cause this? Is it a motherboard issue?

Any help is greatly appreciated

thanks.

most likely not the MB

if the video works fine on external monitors, then you know that the video card and MB are cooperating;
there is a power supply for the backlight that might be dying or the majority of the lcd assembly, which can be messed up from the connectivity bus to the actual pixels themselves
i think you can replace either the backlight PS or the whole screen assembly
or just keep using an external monitor