I can log into cPanel and into AMP, but when I get to the box "Log in to Plesk Sitebuilder 4.5.0 for Linux/Unix", it will not accept my login name or password. I have reset my password *many* times. I am attempting to set up my website for the first time.

At the AMP Builder Login, the User is already filled in with a name I was assigned by you. I put in my password (the only one I've used here) and the Plesk login page/box opens up. I enter my user name and password, and I get the error: "Invalid user name or password. Please reenter your user name and password or use the Forgot your password option."
I've gone through the forgotten password several times to reset it - it never allows me in to the Sitebuilder program.