When Ubuntu starts up, the back-light is off on my laptop.

I have a acer Aspire 4736Z Laptop

Same problem with my laptop: emachine G725

found any solution..?

Try the boot option:

acpi=vendor

May help

i am new user of ubentu can you explain how to use this boot option please

Instead of asking, why not wesearch a little. This will not only teach you a little about your OS, but it will also accelerate the fix as you are not waiting for someone to guide you.

If you run:

gksudo gedit /etc/default/grub

You can find this line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

change it to:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=vendor"

Save the new file, close gedit and run:

sudo update-grub

Reboot to test

This not help me.... still same problem present.

This not help me.... still same problem present.

Dear still the same problem

Dear still the same problem

Did you try the workarounds suggested in bug 765438?

(1) https://bugs.launchpad.net/ubuntu/+source/linux/+bug/765438/comments/2

(2) If that doesn't work, you can try the workaround described in the bug's description, i.e., after booting, run this command (in a Terminal window or virtual console) to manually set your backlight to the highest brightness:

sudo setpci -s 00:02.0 F4.B=00

(If that works, you can set up your computer to run that automatically as part of the start-up process.)

(3) If that doesn't work either, you can try using a patched kernel and power manager, as described at https://bugs.launchpad.net/ubuntu/+source/linux/+bug/765438/comments/11.

(4) If that fails, and you're on a 2.6.38-series kernel, you can downgrade to the 2.6.35-series, which does not seem to have this problem (or does not have it as often).

If you have trouble implementing any of these workarounds, please feel free to post another reply in this question to get help.

Dear

I am a new user of ubentu please help me how to do this..?

Try workaround (1) first. You can test out the acpi_osi=Linux boot option before actually adding it permanently. See https://help.ubuntu.com/community/BootOptions#Change%20Boot%20Options%20Temporarily%20For%20An%20Existing%20Installation. If you have trouble following those instructions please post a reply explaining as specifically as possible what the difficulty is. Once you boot, if your screen is still not lit up, you must use the buttons, keys, or key combinations on your computer that are supposed to adjust brightness. If they are ineffective, then that workaround was not successful for you and you should move on to the next one (if you need help with that, please post a reply).

how can i access the boot menu if the backlights isn't turned on? i can't see anything....
and please.. i don't know anything about programming or something like that and i can't understand what the code means..

@exrvs
I'm assuming you're attempting the workaround detailed at https://bugs.launchpad.net/ubuntu/+source/linux/+bug/765438/comments/2.

You can see what's on the screen without the backlight under some ambient lighting conditions. If you can't see it like that, then you can attach an external monitor. (If you don't have one, perhaps you know one who does, or perhaps there is one you can use at work/school/wherever.) Alternatively, if you are trying to fix the problem on an installed system (rather than on a live CD), you can boot from a live CD of a different version of Ubuntu that does not have the problem, and use that to edit the file on the installed system.

For help editing boot options, see http://ubuntuforums.org/showthread.php?t=1613132. You can choose whichever method you want (so long as it is consistent with your system--for example, methods that say "not wubi" cannot be used on a Wubi system, and methods for the live CD cannot be used on an installed system).

In the future, when posting in a question started by another user, please only click the "Add Information Request" button if you are requesting information from the user who posted the question, which you intend to use to answer their question. If you are posting in a question but do not want to change the status of the question (as in this case), please instead use the "Just Add a Comment" button.