I have been stumped for the last two days with my Ubuntu install. I naively upgraded to 11.04 without checking the Ubuntu release notes... Turns out their is a known bug affecting Ubuntu ARM installs.

<!-- more -->I upgraded and low and behold, black screen....When I rebooted I could see the Ubuntu logo then poof, darkness. I borrowed another PC and Google'd a bit and found some forum discussions. One that got my attention was http://ubuntuforums.org/showthread.php?t=1742352,

The fix suggested on there is to do the following: Code:

sudo gedit /etc/default/grub

Edit the two lines (GRUB_CMDLINE_LINUX_DEFAULT and GRUB_CMDLINE_LINUX) to read as follows: 

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor vga=792"

sudo update-grub
#need to reboot
#sudo reboot

I modified the suggestion a bit when it didn't work following https://help.ubuntu.com/community/BootText and added the last bit vga=792. At first that didn't work either and I was reading around on the ubuntu help pages here https://wiki.ubuntu.com/Kernel/Debugging/Backlight  and it mentioned that there may be a problem when using AC but on DC it disappears or visa versa so I unplugged my laptop's charger and nothing happened, for a moment. I randomly tried to increase the brightness and voila... it shines! My backlight is back and after a reboot to test it, it all works fine. if the above fails try Code:

echo 9>/sys/class/backlight/acpi_video0/brightness

It didn't work for me but there was a report of it working for others on the Ubuntu forums.