Maybe if you showed us the output of df -h and/or (as root) fdisk -l, we might be able to help you a little more. I haven't seen hd0 used as a label on a disk for a while, then again, I may be mistaken, it still may be around. But I would think that a recent Debian distro would have their hard disks labelled a sda, sdb sdc and so on.
With fdisk -l, we might be able to see if the error is referring to another partition or point us in another direction.

Edit: Was just looking around and it seems it's some kind of grub2 error. You might have to wait for someone who has an Ubuntu install running to help you. I'm not that familiar with Ubuntu's Grub2. I'm just wondering if your booting with a usb stick inserted, or, and external HD attached that's causing your error.