Passwords and Usernames

I’m having some trouble with passwords and usernames and e-mails.

I can enter my website; I know the username and password.

I can enter the .org Forum; I know my Forum Username and password (although I have some trouble with the Forum accepting my password.

However, I’m trying to get into WordPress.com (for a widget download) and it doesn’t recognze my username, password or e-mail.

How can I confirm all of this information? Please!