I wanted to install Ubuntu 12.04 on my external 80 GB hard disk. During installation I selected "Something else" option. I formatted the hard disk there with "free space" as file system. As there was a power down, my computer switched off. Now, its not detecting my hard disk anymore. Though my BIOS shows my external hard disk is connected, but neither Windows nor Ubuntu ( in the "something else" part) detects my hard disk. Please help.
Try accessing Gparted from the live cd and seeing if the External Drive is visible from there. If it's visible format it again and try to install Ubuntu on it again. There could be an error on the hard drive if the computer shut down halway through formatting/installing.