When you raise or lower a laptop lid, a switch is activated to signal whether it is being opened or closed. The screen should naturally shut off as it is being closed, and as it is being turned on, the video adaptor is activated and the backlight brightens the screen. If the screen doesn't brighten, it is possible that a software problem is causing the blank screen, but in most cases it is a hardware issue.
The video card provides the display to the laptop screen. If it is malfunctioning, the screen will be pitch black. It you look closely at the screen and can see a faint image, there is nothing wrong with the video card. One way to test this is to hook the laptop to an external monitor. The video card should be able to display the desktop on the secondary monitor with no problem. If you determine that the video card is the cause, check with the manufacturer to see if it is repairable. In older laptops, the video card is soldered down and cannot be replaced without replacing the entire motherboard.
The close switch is usually located near the area where the lid connects to the base of the laptop. It is triggered as the lid is being closed, and can be triggered prematurely if there is dust or debris in the way. You must open your laptop to see if there is anything that's interfering with the switch's normal operation.
If the screen appears black but you can still make out a faint image in the background, you most likely have a bad backlight. The backlight provides enough brightness to the screen to make it easily viewable even in low lighting conditions. Replace the backlight with one from a known working laptop to diagnose the problem.
The inverter is a flat board that sits just below the monitor and above the keyboard. It connects directly to the backlight and provides power to it. Therefore, if you have a faulty inverter, the backlight will not work. This is often confused with having a bad backlight because the symptoms are usually the same. A bad backlight sometimes will produce distorted colours on the screen. This is the only way (other than replacement) to know whether the problem is being caused by the backlight or the inverter.
There are data and power cables that connect your screen to the motherboard. If these cables are loose, not only will you encounter a blank screen, but it will also flicker or shut off when the lid is moved. A quick fix for this problem is to open the lid to greater than a 90-degree angle before turning on the laptop. This is a temporary fix, however, and the problem will gradually worsen as the cables continue to slip out. Instead, open up the laptop and check to make sure all connections are secure.