Can't login to MacBook Pro because keystrokes are repeated!
Try looking at the InitialKeyRepeat default for the sudo account. I had the same problem, and noticed this that for my user account defaults read -g InitialKeyRepeat returned a value of 25. But sudo defaults read -g InitialKeyRepeat returned a value of 5, which is much faster. I changed the value for sudo using this command:

sudo defaults write -g InitialKeyRepeat -int 25


and I no longer have a problem typing my password at the logon screen. This page is helpful for more details.