Can't login using "nvidia"

I boot up and try to use the password “nvidia” to log in but it keep turning back to the login page,did I do anything wrong?how to fix it?

Is this the GUI only, or is the same true for ssh login? If you have serial console or ssh login, what is the output from:

ls -l /usr/bin/sudo

Also, have you just recently flashed?

thanks a lot