need a way around opening

Boot to root recovery mode (hold shift at boot, select recovery mode, then select root).
type:

cd /home; ls

and press ENTER

You wil now see the users on the system. You can now type:

passwd foo

(replace foo with the user name/s you find and set their password/s).

You can now reboot by running:

reboot

You can now let the system boot normally and log in as expected.

You have a couple of options:

1) The fast way: Add yourself as a new user

When you turn on the computer, hold down SHIFT until the GRUB menu appears.

Use the up and down arrows to select the first entry that has (recovery mode) at the end, e.g.:
Ubuntu, Linux 2.6.31-19-generic (recovery mode)
and press ENTER.

You'll soon get a blue screen with a grey Recovery Menu on it. From it, pick:
root Drop to a root shell prompt

At the bottom of the screen, a command prompt will appear.

Create a user account for yourself by entering:
adduser joey (or whatever you want your username to be)
Enter the password you'd like at the two prompts.
Enter your full name when prompted; the subsequent details are optional.
If you've entered everything correctly enter y when asked if everything is correct.

To make yourself an administrator, at the command prompt, type:
usermod -a -G adm,dialout,cdrom,plugdev,lpadmin,admin,sambashare joey
Obviously, this assumes a username of "joey"; change if necessary.

You can check you've been added to all the groups, by typing:
groups joey

When happy that you're now an admin, type:
shutdown -r now
to restart.
You should now be able to make all the changes you want.

2) Slower, but possibly better long-term: reinstall Ubuntu
Download the latest version from:
http://www.ubuntu.com/desktop/get-ubuntu/download
Follow the instructions on that page for CD creation/installation.