Registrars are responsible for the administration of the domain names in their portfolio and for the technical implementation of domain names. In order to function properly, your domain name must be referenced by one or more name servers. A name server associates a domain name to a mail server, web server, etc. The association of this technical data should be kept up-to-date by registrars in so-called zone files.
Please contact your registrar to verify that the zone file has been transferred or updated.