If you just added this site in the control panel, it may take a minute or two for Apache to restart.
Also... Make sure you actually added this site in the control panel. Setting your nameservers isn't enough!
No worries. Go here to pay your bill and we'll have you back online ASAP.
Didn't get a warning? You might want to tell us your new email address. :)
One more thing to try: Are you sure it's spelled right?
If none of that helps, contact support. We'll figure it out!