UNIX for Advanced & Expert Users

Hi,
When I installed Ubuntu on my laptop, I had chosen "automatic login" . So i was not asked ofr username and password everytime I switched on. I later wanted to change the settings. So I went to systems-->administration-->login window-->security. There I disabled automatic login and I reboot the computer. Now the GUI does not allow me to enter USername and password. It says "Authorization denied" at the login screeen.. PLease help me.

At login screen press alt+ctrl+f1 and login into console. There - log in and use "startx" command. I hope (wild guess) this works as I don't have a Ubuntu at hand at the moment. If it does - go to the options and review them.

Another workaround:
if you installed grub as boot loader, you can edit the kernel parameters before booting via grub. Add a 'init=/bin/sh' parameter, and boot. That gives you a root shell. Remount the root filesystem, like 'mount -o remount,rw /'. create the user account you seem to be missing (useradd, see manpage). remount the file system readonly, like 'mount -o remount,rw /'. exit the shell, aka reboot. That should have created a valid user.

I do not know Ubuntu that well, but that should work generically on any linux which has grub. W/o grub, you can achieve the same if you have a boot CD somewhere.

At Grub choose "recovery mode" as the choice and it should drop you into a prompt and you can reset your password there using "passwd username"

If that doesn't work try these links:
How to reset your password in Ubuntu
How-To Recover password under Ubuntu|Ubuntu Geek