Ubuntu – “Can not mount /dev/loop0” during install from CD

The checksums (MD5) can be found on releases.ubuntu.com. I would suggest you do the following:

1. Check that the MD5 checksum of the ISO image you downloaded matches the one in the aforementioned link, by following these directions.
2. If that looks okay, boot the CD and press the Spacebar key when you see the keyboard icon in the bottom-center of the screen. Select your language, then the "Check CD for defects" boot option.

If neither of those produce any errors, please file a bug here, following these instructions to attach /casper.log to it.

Other distros had at same time this same problem, despite of installation-CD or DVD ... apparently it was forgotten to include the package of xserver-xorg in the installation-process.

If protected-mode is possible, you could try to install xserver-xorg by running the following command:

sudo apt-get install xserver-xorg*

After this, run the following commands in protected mode (Strg + Alt + F1) and install the graphics-drivers suiting to your graphics card.

sudo apt-get install fglrx-updates fglrx-amdcccle-updates fglrx-updates-dev
sudo aticonfig --lsa
sudo aticonfig --adapter=all --initial
sudo reboot

After reboot is finished, run the following command in protected mode too with (Strg + Alt + F1):

sudo aticonfig --adapter=all --odgt

Now it should work...