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i have runned an ubuntu update from 11 to 12.4 and when the computer restarted the ubuntu logo showed quickley, then the black screen with the mouse icon active with the wait circle rotating continiously. i try to boot from the old ubuntu 11.00 cd and the same thing happens. any keyboard combination for a safe boot or any suggestions please ?

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I believe you need to use nomodeset, i use it on my laptop, I can't boot any linux distro without it.

When Ubuntu boots for the first time, you'll see a purple screen, press f6 and use nomodeset option, you could also use acpi=off, i only use nomodeset`. If that works for you, go on and install ubuntu, When you're done restart the PC.

When you restart the pc, you'll see a grub menu, scroll on ubuntu, press e now you can edit you're grub menu.

Scroll Down to the word quiet or quiet splash and add the word nomodeset at the end of that line. Press F10 to boot. Assuming everything is ok, ubuntu will start correctly.

To set nomodeset permanently open a terminal, write gksudo gedit /etc/default/grub and enter you're root password, add the options that you need, like so:

GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nomodeset"

Or maybe

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nomodeset acpi_osi=\"Linux\""

Save the file, and write in the terminal sudo update-grub


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