What is the model number Alex? It's on the bottom of the laptop.
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From your brief 'diagnosis', suggests there is a problem with the Video Cable.
1) Either loose at the motherboard, or loose at the screen Inverter,
(IF USED), or loose at the back of the LCD screen.
2) Video Cable is damaged. Stretched/Broken wire inside.
Suggestion would be to PHYSICALLY check the Video Cable's connections.
Visual inspection alone will not do. To -> Ensure the connections are tight, you have to physically try to plug them in tighter.
Do not, of course know what laptop we are talking about here.
(And only presume we are talking about a laptop; and an Asus one at that, because of the problem heading)
The Video Cable plugs into the motherboard, either in an area under the Keyboard; or under the Switch Cover.
(It can also plug into the bottom edge of the motherboard)
Believe easiest way to start off here..........
The Switch Cover is a thin strip of plastic, above the Keyboard; and under the Display Assembly.
Usually has the Power On button in it, indicator LED lights; and speakers. (IF option)
Later designs of laptops did away with using a Switch Cover, and went to just having it as part of the Palm Rest Cover, itself.
Further designs of laptops, also have the Power On button in the side of a Hinge. Usually the Right one.
From the motherboard, the Video Cable then typically routes by the Left Hinge.
Then it goes up into the Display Assembly.
IF a screen Inverter is used, one small cable comes off the Video Cable; and connects to one side of the screen Inverter.
The rest of the Video Cable goes on to connect to the back of the LCD screen.
A screen Inverter is used for CCFL backlighting.
(Cold Cathode Fluorescent Lamp)
GENERALLY, a screen Inverter is not used for LED backlighting.
(Light Emitting Diode)
If no screen Inverter is used, the Video Cable goes on to connect to the back of the LCD screen.
May be a small cable from it to the LED backlights.
From normal repeated opening, and closing of a laptop, the Video Cable may become pinched, and/or pulled on.
(Goes by the Left Hinge)
This can cause loose connections, as described above; and/or cause damage to the Video Cable.
(As described above)
If connections are found to be tight, then Video Cable is removed, and checked for Continuity.
A continuity test is performed with a multimeter, set to OHM's. (1K)
Each wire in the Video Cable is checked for continuity.
(In a continuity test, the multimeter sends electricity through the wire. Positive (Red) probe lead of multimeter to one end of wire, Negative (Black) probe lead to other end of wire.
It isn't the amount of the Resistance you are looking for, so much; it is JUST to see if you get a reading at all.
No reading on multimeter suggests there is a broken wire.
Also an assistant should be used, to gently wiggle the Video Cable; to see if you get an intermittent reading.
If so, this also suggests a broken wire.
You can take the Video Cable down to the nearest computer repair shop, and have the resident tech check it for a couple of bucks.
(If they do not know how to perform this simple test, GET OUTTA THERE. They are parts changers, and not tech's)
You may opt to simply replace the Video Cable.
Costs usually ranges from $4 to $12.
Have seen examples though, that may range $35.
That's about it for me until I have the model number.
NOT stating I can guide you step by step in these procedures, because it is an Asus.
Thank them for that. They do NOT like to release any info, such as a Service Manual, to the general public.
This antiquated type of thinking could run them out of business, IMHO.
HOWEVER, with your patience, and both of us conversing back, and forth in Comments; I have great expectations that I CAN guide you step by step.
'Ain't my first barbecue'
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Some additional pictorial info that may help,
Asus Eee PC 1201n, and showing LCD screen side of Video Cable connection,http://www.insidemylaptop.com/replace-broken-led-backlit-screen-asus-eee-pc-1201n-netbook/
With the style below, the Keyboard, Palm Rest Cover, and a metal Static shield need to be removed; in order to access the motherboard connection, of the Video Cable,http://www.insidemylaptop.com/disassemble-asus-eee-pc-1215b-laptop/
Scroll down to the last photo.
At the Top/Left corner there is a Yellow Arrow, which points to the motherboard side connection, of the Video Cable.
(Of this particular style of laptop)
Video Cable example for Asus Eee PC 1215P,http://www.ebay.com/itm/NEW-ASUS-Eee-PC-1215-1215N-1215P-1215T-LCD-Video-Cable-1422-00SF000-/251214440310?pt=LH_DefaultDomain_0&hash=item3a7d8c2776
Two views are shown of the same cable.
The wide White connector at Top, with the goldish Mylar plastic on it, is the LCD screen side connector.
The smaller Black connector shown at bottom plugs into the motherboard. The small Black wire with the eyelet terminal on it, connects to a Ground screw.
No screen Inverter is used with this model.
The laptop uses a series of LED's for a Backlight,https://www.laptopscreen.com/English/model/ASUS/EEE~PC~1215B/