If Ubuntu is the only installation and you don't normally get a grub screen, hold down the shift key during boot up. If you have more than one OS installed grub will show and all you have to do is select the recovery option for your Ubuntu kernel. You don't need a password here, you get sent to a menu system.
Originally Posted by bobmunro
In 12.04 console, to make the root drive writable I have had to run a fsck check on the drive (one of the menu options), the drive gets changed to writable when you do, this is necessary for the next step to fix the password. Not sure about 12.10 I am assuming it hasn't changed.
After the check completes return to the menu and select "Drop to root terminal", or worded very similar, the root terminal is what you need. In the root terminal enter the following commands,
This is only to check the drive is mounted, you will see user home folders if it is. Not entirely necessary, I use it as a precaution for if the drive is not mounted the next command will fail.
You will be asked to enter a Unix password and confirm it by entering it again. If the 2 match OK your password will now be set on your user account. Cheers.
Edit: type "exit" then press "Enter" to get back to the menu from the root terminal. IIRC the top option will let you then continue a normal boot. Or type "reboot" and press "Enter" (don't include any quotation marks with any of the commands in this edit).
Edit 2: I just noticed your bean count and join date, welcome to the forums