Have you tried checking the email you recieved when you registered, to make sure you typed the password exactly as it was shown when you registered?
Did you accidentially press space when you shouldn't have when you typed in your password?
Have you made sure that "numlock" and "capslock" were off when you typed everything in?
Maybe you could give more info on what exactly happened when you tried logging in, it would make it easier to help you.