You *did* have a password on Ubuntu, it's impossible to install the OS without one. I'd suggest you reinstall Ubuntu and make a note of the password when you provide it. Note that Ubuntu 12.10 is out now, so you'd probably benefit from giving yourself an upgrade too.
I don't understand how you say you "completely erased" the computer and are surprised that it doesn't boot...??
The boot error appears to be a failure to boot from the network, so it's already failed botoing local disks. as it's blank apparently.