Make sure that you don't have your Caps Lock on and be extremely sure that you typed your username and psw correctly.
Though, it is possible that someone tried to access your account and requested a new psw for you. Check your email for a new password.
Or you can request a new password by yourself. It will be sent to your email.Edit:
Here's a pic that shows from where you can request yourself a new psw (click on image to enlarge).