You have to diagnose the problem.......
Right off hand I would say the screen Inverter is bad, but this is just guessing......
Because your laptop may not use a screen Inverter.
It may use LED's as backlighting.
Or, it may have a pinched/damaged video cable.......
An LCD screen cannot produce light. It needs an additional light source.
A Backlight is the additional light source.....
A Backlight can be a CCFL, (Or more than one), or a series of LED's.
(Light Emitting Diode)
A CCFL is a Cold Cathode Fluorescent Lamp. (Bulb)
Similar to Fluorescent lighting used in homes, and businesses; but on a MUCH smaller scale.
Average thickness is 2mm. That is a little larger than 1/16th of an Inch, or about the width of this capital letter -> O <-
Average length is almost as long, as the LCD screen is in height.
A screen Inverter is used to convert the power, (Electricity), of the laptop; for the LCD screen, and the Backlight.
A laptop that uses a CCFL, (Or more than one), uses a screen Inverter.
A laptop that uses LED backlighting, May or May Not use a screen Inverter.
Seems when the LED backlighting technology first came out, a few laptop models Did use a screen Inverter.
As the LED backlighting technology evolved, a screen Inverter was no longer used.
Average example of a screen Inverter,http://www.amazon.com/Screen-Inverter-HP-Pavilion-DV6000/dp/B0058TMLLY
The LCD screen is in the Display Assembly.
The plastic frame in front of the LCD screen, is the Display Bezel.
(Different manufacturers use different terms. The above is for HP, and Compaq laptops)
Display Bezel removed, the screen Inverter is located at the bottom of the LCD screen.
That is IF, the laptop uses a screen Inverter.
If the Backlight is bad on a laptop that uses LED backlighting, the LCD screen itself is replaced.
The LED backlighting is built-in.
The Video Cable, (Display Cable, etc), connects to the motherboard, usually under an area under the Keyboard, or just above it. Some models have the Video Cable connecting to the Bottom of the motherboard, and at the back.
Average example of a Video Cable,http://www.amazon.com/Video-HP-Pavilion-DV6000-FOXDDAT8ALC0041A/dp/B003YDLDBK
The Video Cable then routes through Channels, and Latches; and comes up around the left Hinge.
It then goes on to up into the Display Assembly.
Depending on the technology used, (screen Inverter, or no), the Video Cable splits off, and connects to the screen Inverter.
The rest of the Video Cable then connects to the back, of the LCD screen.
Due to just normal opening, and closing of the laptop; the Video Cable may become pinched, and/or pulled on.
This can cause the connection at the motherboard to become loose, and/or at the screen Inverter, (IF used), and/or at the back of the LCD screen.
It may also cause damage to the Video Cable. (Stretched/Broken)
1) May be just a loose connection/s of the Video Cable
2) May be a damaged Video Cable
3) May be a bad screen Inverter
4) May be a bad LCD screen.
Post in a Comment, as to the laptop manufacturer name, and model number.
This way I can step by step you through diagnosing the problem, for YOUR laptop; and not post a bunch of generic information.
HOWEVER, it does depend on if the information is available on the internet. Such as a free Service Manual, and/or pictorial guides.
I CAN guide you even if there is not, but if there is; it just makes it simpler for you.
I can tell you it is easy. Once you have performed this procedure, you may want to do it for a friend, or relative; if the situation arises.