We need a little more to go on. Are you using SQL authentication or Windows authentication? Typically "login failed" means you have the wrong combination of user name and password. Make sure you are using the proper authentication method, either local SQL or Windows.
I'm guessing that the first login was successful, but subsequent logins using the same credentials weren't, which would mean that the account was set up with "change password on first login" set (using the GUI), or with the option "MUST_CHANGE" (if created using T-SQL).