Screen light won't turn off

Perhaps it's the backlighting or the switch that controls the on/off of the display when the laptop lid is opened/closed. Take a look at this video to help troubleshoot: http://www.youtube.com/watch?v=2Yi6GNFcP3w

1) Looking at the User Manual right now, and do not see a Hot Key on the Keyboard, that shifts the display.

[ Hot Key is also known as Special Key. The F1 through F12 keys at the top of the keyboard, and also for your model, colored keys on the keyboard ]

It could be the Screen Resolution is messed up. Not set at the correct settings.

Right-click on an empty area of your desktop screen.
At the bottom of the drop down list, click on Properties.

In the Display Properties window click on the Settings tab.

The screen pixel resolution should be set at 1366 X 768,

http://www.screentekinc.com/Asus_EEE_PC_1201HAB--12.1-inch--1366x768-wxga_hd-laptop-lcd-screen.shtml

In the middle of the Display Properties window, you see the blue subheading - Screen resolution

Right under this small subheading is a Slider.
The Pointed 'arrow' with the green tip, and top, slides back, and forth on the 'line'.

It should state 1366 X 768.
If it does not;

A) Left-click on that green tipped Slider. Hold the left mouse button down. Move your mouse, and move the Slider. (Drag)
Move it to the Left to Decrease the screen resolution, or to the Right to Increase the screen resolution.

Can't set it to 1366 X 768? Post back in a Comment.
ALSO, the Color Quality should be set to -
Highest (32 bit)

If not click on the blue down arrow to the right of this box.
In the list left-click on Highest (32 bit)

Now go below to the right, and click on Apply.
After go below to the Left, and click on OK.

Still no joy?
Believe the problem is hardware related.

Could be something as simple (?) as a bad Video Cable.
(Goes from the motherboard, up under the left Hinge, and then up into the Display Assembly)

Could be the screen Inverter.

However the Eee PC 1201HAB is supposed to use an LCD panel, that has qa series of LED's for backlighting.
Newer backlighting that uses a series of LED's for the Backlight, doesn't require a screen Inverter.

There were some LED backlit LCD screen, that DID use a screen Inverter. Mostly the older models of laptops.
This is what makes me think your LCD screen's Backlight, (And LED), may use a screen Inverter,

http://www.batterystyle.com/asus-eee-pc-1201hab-screen-p-168219.html

Scroll down,
"5. Disconnect the power cable and video cable from the Asus EEE PC 1201HAB Lcd panel. The power cable connects the screen's power source, the lcd inverter, to the backlight lamp attached to a side of the panel."

Probably just a generic form, and didn't take in consideration that the Eee PC 1201HAB netbook, uses a series of LED's, as a Backlight.

May not have a screen Inverter.

To explain;
Primer:

An LCD screen cannot produce light by itself,

http://solutions.3m.com/wps/portal/3M/en_US/NA_Optical/Systems/BehindTheScenes/Optics101/

(Click on the window with the computer monitor in it )

It needs an additional light source. A Backlight is the additional light source.
A Backlight can be a CCFL, (Or two of them), or a series of LED's.

[ LED = Light Emitting Diode.
CCFL stands for Cold Cathode Fluorescent Lamp.
Similar to Fluorescent lighting used in homes, and businesses, but on a MUCH smaller scale.

{Average thickness of a CCFL bulb is 2mm. That is a a little larger than 1/16th of an Inch.
The average length is almost as long, as the LCD screen is in height]

A screen Inverter is used to CONVERT the power from the laptop, for the LCD screen, and Backlight.

Do not see any listings for an Asus Eee PC 1201HAB netbook, for a screen Inverter. Believe the LCD screen uses LED's for a Backlight, and does NOT use a screen Inverter.

Which means if the problem is in the Display Assembly, the LCD screen itself will need to be replaced.
The LED backlighting is built-in.

[Hmmmm, I see a trend going on here that I do not care for, and just woke up to it. Have to replace the entire LCD screen, and cannot just replace the Backlight, or screen Inverter? Sounds like Ka-ching $$$$$ for somebody!

A screen Inverter usually averages from $20 to $40+.
A Backlight ( CCFL) usually ranges from $10 to $15.
An average LCD screen can range from $80 to $300+.]

How to know if the problem is in the Display Assembly?
Use a VGA monitor, and connect it to your laptop.

A) Laptop OFF, monitor OFF. Connect a VGA monitor's cable to the VGA port on the laptop.
(Left side rear. This is an example of a VGA Cable, and VGA connector { Port on a computer },

http://en.wikipedia.org/wiki/VGA_connector )

You can use an older CRT type of VGA monitor (Looks like a small TV), or a flat LCD screen monitor if it has a VGA cable attached.

B) Turn the monitor on. If a CRT type allow it to warm up.
Turn the laptop on.
By default the display should automatically show, on the external VGA monitor.
IF not;

There are at least three display options:
1) Internal monitor of laptop ONLY
2) Internal monitor of laptop AND external VGA monitor
3) External VGA monitor ONLY

Press the Fn key down, and hold it down. At the same time tap once on the F8 key.
The F8 key is the Display Toggle-Over key.
(Give it a few seconds. Sometimes it doesn't happen right away)

Still no?
Hold the Fn key down again, and tap once more on the F8 key.

Is the display off to one side on the external VGA monitor?
Post back in a Comment.

Regards,
joecoolvette

The drive voltage from the motherboard to the input of the inverter board is missing which in turn drives the backlight, trouble is you will need a service manual to track the problem. Try www.dell.com for customer support and the technical department, they may be able to provide answers.

the screen lamp (CFT) may gone out of order

Maybe you are not giving it enough time to get into the setup.

Let it sit for a while and see what happens.

Press MODE. Use the arrow keys to highlight NORMAL on the first line and press ENTER. Press 2ND [QUIT] to exit the mode screen.

Alternatively, you can set any other display mode on that screen.

When it flickers, can you still see the text when the screen goes dark?
May have to use a bright flashlight set right on the display to see
the text on the screen beside where the light sits.
That will tell you if it's the backlight.

You can also look at a grazing angle into one of the edges to see if the
backlight is flickering when the display does.
When it's cold, does it start with a slight pinkish color? That can be
a sign of backlight going bad.
Anything interesting happen when you flex the cable by moving the screen?

I'm not saying it's impossible, but I've never seen software cause
consistent screen flicker. And if the vga port doesn't flicker, sw is
even less likely the problem.

If you bet the odds, you'd bet on a bad display cable.
Won't hurt to try replugging it.

If that doesn't help, then your monitor may be dying....

Have you tried checking the Battery and Display settings from the main screen Settings menu? There is an option to enable or disable the backlight, as well as set the brightness.

There is also a setting called "Use ambient light sensor", which sets the backlight and keyboard light to only turn on if it is dark when you are using it.