You should use an nslookup tool (like Windows version here) to perform some first-level troubleshooting. Verify from your local computer you can resolve the correct IP address from your current ISP DNS servers. In my case, i am tracking down my domain icelava.net
C:\Program Files\Microsoft Visual Studio 10.0\VC>nslookup
Default Server: dnscache2.singnet.com.sg
Address: 165.21.100.88
> icelava.net
Server: dnscache2.singnet.com.sg
Address: 165.21.100.88
Non-authoritative answer:
Name: icelava.net
Address: 70.85.20.8
> www.icelava.net
Server: dnscache2.singnet.com.sg
Address: 165.21.100.88
Non-authoritative answer:
Name: www.icelava.net
Address: 70.85.20.8
If you have set a CNAME record and is properly propagated, the local DNS server would be able to reply knowing it's an alias
> web.icelava.net
Server: dnscache2.singnet.com.sg
Address: 165.21.100.88
Non-authoritative answer:
Name: www.icelava.net
Address: 70.85.20.8
Aliases: web.icelava.net
If it does not seem right I'd convert the query type to NS to determine what are the nameservers authoritative for my domain
> set type=ns
> icelava.net
Server: dnscache2.singnet.com.sg
Address: 165.21.100.88
Non-authoritative answer:
icelava.net nameserver = ns4.nameresolve.com
icelava.net nameserver = ns1.nameresolve.com
icelava.net nameserver = ns3.nameresolve.com
icelava.net nameserver = ns2.nameresolve.com
ns2.nameresolve.com internet address = 63.251.83.88
ns3.nameresolve.com internet address = 63.251.171.92
ns4.nameresolve.com internet address = 64.94.31.66
If the nameservers do not match the nameserver(s) whose zone file you are editing, I suggest contacting your DNS administrator/provider for more technical details.