@Anonymous User
Welcome to the forum. Could be a few things.
If it's a Roku you're setting up, are you on the stage where you are trying to activate the box online? If so you need to set up a Roku account for that stage, your NOW TV login doesn't work there.
If it's a NOW TV box you have, or you're trying to log into the NOW TV app then if you've recently changed your password to one with special characters in, try changing it again to one with just letters and numbers, and then try again.
Otherwise on the box you already have, open up the NOW TV box and go to the My Account screen and check what username you are signed in as there, make sure this is the username you are using to sign into your new box.
