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I've turned off my laptop while the update manager was installing ubuntu 12.04 LTS. Now when I try to boot into ubuntu the screen is only in blue and I can do nothing execpt to turn it off. Is there anyway to reinstall th OS using the downloaded files? Thanks!

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What happens when you press Ctrl+Alt+F1? – Eliah Kagan Jun 25 '12 at 5:09

Turning off a computer while updating is a very dangerous and risky task. Do not do that unless there is a kernel panic or a power outage.

Now the only thing you can do is to recover all your personal files using a Ubuntu LiveCD and reinstall Ubuntu.

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Today I had a very similar problem -- after updating the system, rebooting and logging in, only the blue screen appeared without any signs of Unity. The way I fixed it was this.

  1. Switched to tty1 (Ctrl+Alt+F1), logged in and made sure that all updates have been applied (sudo apt-get update && sudo apt-get upgrade).
  2. Installed gdm by executing sudo apt-get install gdm. This automatically invoked configuration where I have selected gdm instead of lightdm. Installation of gdm lead to uninstallation of unity.
  3. Rebooted, switched to tty1, logged in, and installed unity by executing sudo apt-get install unity and then ran sudo dpkg-reconfigure gdm where I have selected lightdm this time.
  4. Rebooted, logged in using the graphical prompt and Unity loaded as hoped for.

Hope this experience will be useful.

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While upgrading the system is very vulnerable. Files needed by the system are removed and replaced. Turning of your machine while doing this can pretty much break the system. That's what happened with you. To install Ubuntu now, you'll need to create a live CD or bootable usb drive. Try getting your data off of the hard disk first. Good luck.

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If you believe to be experienced enough you can boot from a live CD and chroot into your installation's root directory and run apt-get upgrade and apt-get upgrade. This sometimes throws errors that allow you to google for a solution or downright give the commands to fix your problem.

If you don't know how to 'chroot' it is probably easiest to salvage your personal files and do a fresh install.

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