DNS single lable hostname problem

Hi all, I just walk on a situation and I need help. DNS is not working and I can see this error in the log file of the DC and this seems to be there since the domain was created a year ago.

"The DNS server machine currently has no DNS domain name. Its DNS name is a single label hostname with no domain (example: "host" rather than "host.microsoft.com").

You might have forgotten to configure a primary DNS domain for the server computer. For more information, see either "DNS server log reference" or "To configure the primary DNS suffix for a client computer" in the online Help.

While the DNS server has only a single label name, all zones created will have default records (SOA and NS) created using only this single label name for the server's hostname. This can lead to incorrect and failed referrals when clients and other DNS servers use these records to locate this server by name.

To correct this problem:
1) open Control Panel
2) open System applet
3) select Computer Name tab
4) click the "Change" button and join the computer to a domain or workgroup; this name will be used as your DNS domain name
5) reboot to initialize with new domain name "

When I look in the DC, the name of the domain is "mydomain" instead of "mydomain.com".
The DC does not let me change it (properties is not available and the msg said we cannot do it because this is a DC).
Do you have any idea how I could fix this? DCPromo (demote) is not really an option.

Thanks.