1.) Check SIP Server Domain Name/IP address. Make sure you have the right Name or IP address.
2.) Check the web browser and access the configuration menu. Make sure that the SIP Server Domain Name/IP Address is correct.
3.) Check the register status under SIP Account Settings in the configuration menu (from web browser). If your status is "Not Registered", it means you do not have a SIP account. Contact your SIP service provider to get an account.