Wilton,
Since you've mentioned a new domain controller, i'll assume that you've
succesfully promoted the "new" DC into the old DC's domain with success. If
what you did was create an entire new root DC in a different, unique domain,
you'll have to reinstall or at least demote, join + promote new server into
target domain.
A new DC will receive the schema and all relevent accounts, containers
on the domain through replication. What it won't receive automatically is
the 5 FSMO roles (these need to be transferred manually) and any non-profile
shares + applications that the users are relying on. If you rely on DNS
resolution, you may need to install DNS. Same goes for other services like
DHCP.
If the new DC is a new Root, you are recreating the domain from scratch.
Regardless of whether the FQDN concurs.