DNS Reslove?

Ok, I have built a uploaded a client’s web site, if i use the IP address in my browser it will come up fine, if I use the url it doesn’t relsolve, tracert has the same problem, tracert will not work for the url, but will work fo r the ip, when i go to samspade.org I can use both ip, and URL, nslookup doesn’t reslove with IP, or URL, we updated the site last week with the correct name servers, what i would like to know is how to determine who is dropping the ball, what name server is it getting dropped at and why.