Are you getting the cpanel login box to appear or are you not even getting to that step? If you can get to that step, than perhaps your password is wrong, which is a problem you can fix by reseting it with the password reset link that should appear after 3 failed logins.
If all else fails, you can contact support and they can look into the problem. However, try visiting cpanel at this link:
http://72.29.89.97:2082
and using the information you got in your welcome letter. If it doesn't let you in, try to reset your password. If that doesn't work, contact support at the help desk:
http://desk.surpasshosting.com