Problem adding additional Domain controller for existing domain

Hi Friends,

Im having hard time trying to add additional server to my existing domain controller..i’ve configured the DNS look up zone and the ADS installed..i want another server as additional server but when i try to add..it asks for “username, Password & Domain” i add these and click next..it goes to next window box, ther it tells me to put FULL dns name..but when i put full dns name i.e test.server.com its not taking neither server.com keeps telling me unable to contact and ther’s no domain for that ip, i dont understand why this is happening, if anyone can help me through would be glad.