Seems like like you did not authorize the DHCP Server in active directory. If so, open DHCP Console, right click your Server and chose authorise.
First, check, if you can ping your DC using the FQDN and the ip. If you can't reach it by name, check the DNS Settings of the DHCP Server.
If there is no need for DHCP in your network or you already got one on the DC and do not need redundancy, you can disable the service on the server.