well, the from address:
HireNurses.com
is only the domain, it does not include the user account. The from address must be a full email address:
person@HireNurses.com
I'm betting that in the authentication settings, you also don't include the full email address. The authentication must be a full email address for the domain and include the password
The SMTP server is refusing the username and password you entered, so you should check with the HOST to determine what username and password should be used.