I would first try to reboot and enter single user mode. The boot loader is generally not password protected by default.
1) If you are using grub you would highlight the OS you want to boot to and press e to edit the line.
2) Select the line that starts with kernel and type e to edit the line.
3) Go to the end of the line and type single as a separate word (press the [Spacebar] and then type single). Press [Enter] to exit edit mode.
4) Back at the GRUB screen, type b to boot into single user mode.