alt key?
reboot your MacBook Pro to the recovery partition by holding Command-R during a restart.
You can reset a firmware password (if that is activated) by clicking the Utilities menu/Firmware Password. If the next window asks you to Activate the firmware password, then you don't have one. You can then quit that utility, then open the Terminal, and type reset password, and press enter. That will bring up the password utility. Choose your drive, and select the user name, and you can change the password for that user.
But, I more suspect that something else has happened, and you might want to quit that password utility, then choose Reinstall OS X, and continue with a reinstall of your system.
You need an internet connection to do this. This reinstall will (probably) not lose any of YOUR files, and should simply reload your Lion system.