What can I do when Ubuntu 11.10 doesn't recognize my password?

Question

Currently I'm dual-booting Ubuntu along side Windows 7. I recently upgraded to 11.10, and everything was going fine for a bit. However, I can no longer log in with my user account. The guest account works fine. I also tried logging in through the command line (Alt+Ctrl+F1), but to no avail. For some reason it doesn't seem to recognize my password anymore.

Also, I no longer see the secondary GRUB screen:

Instead it will flash a Fatal Error message, then load the GUI. I'm wondering what my options are, I don't have anything important on there that I don't have backed up, so I'd be fine with re-installing Ubuntu entirley.

Answer 1

If Paul's answer doesn't work, you could boot a LiveCD (of Ubuntu), log in as root to the LiveCD and do this:

mount your normal Ubuntu partition (mkdir /mnt/ubuntu && mount /dev/sda1 /mnt/ubuntu)
chroot into it (chroot /mnt/ubuntu)
change your password (passwd my_user)
reboot

Answer 2

Hold down shift during boot up. This should cause the grub menu to appear. Choose the recovery mode, which will drop you into a command prompt. At the prompt, type

passwd <user>

Where user is your normal userid. This will prompt to change the password. Then you can reboot and login as normal.