I use fedora but the commands should be the same.
First reboot
Then when the grub srceen appears press "a", then add a 1 to the end of the kernel line. It should boot to a terminal prompt
Type in the command "psswd root"
From there you should be able to reset the password.

Yes, sorry, the command I gave "psswd root" should have been passwd. Geez, there should be a spell check for Linux commands. Heh.