There are generally four problems that occur with LCDs and there a couple of easy tests to judge what part may be causing the problem.
First is the ever popular cracked screen. This occurs when blunt force trauma causes the front glass or the liquid crystal panel to break which can cause the liquid crystal to start oozing out behind the front glass. This usually starts a spider web looking pattern from the impact point and puddles of the liquid crystal to form blocking the picture from the screen. This will require a new LCD and usually stops there if that is all it is doing.
The second biggest issue is the backlight. Typically, this is diagnosed when you look real close to the screen you can still make out a picture, but it is extremely dark and changing the brightness does not help. The backlight in the LCD itself generally will have to be replaced, another cause may be the logic board but only happens if there is a short somewhere or there is spill damage.
The third issue is just a solid white or gray screen. If the machine still boots up, but there is no picture, this means your backlight is working fine, but there is something wrong getting the picture up to the LCD.
The last issue is the completely black screen with no picture, no backlight, just nothing. This problem may be caused by a faulty LCD, but leaves us with the logic board which more often than not is the culprit in this situation. The most common cause for this is a dead graphics chip.
I hope this clears things up, and hopefully you’ll have a good starting point on diagnosing your own LCD problem.