Did you install a new keyboard layout? If yes, then you are probably typing in the wrong password.
Keys may have moved with the new layout.
You can try this, at the login screen, press Ctrl + Alt + F1 ( three keys together ) and see if you get a command prompt. If yes, enter your user and when prompted, password. If that works, then your keyboard layout in the gui session is probably changed.
Not sure of what you want to wind up with. If you don't want the new layout, you would have to remove the the package that changed the layout.
This might help. There is a Amharic machine that translates English to Amharic. You could try your old password, and see the Amharic translation. That might work. The link..