It sounds as if you installed a version of Red Hat Enterprise Linux but have not registered it/configured it with a valid license key (needed for updates).
Is this a new installation? Do you have a subscription to the Red Hat Network for updates for that computer?
If you have not purchased a subscription for updates--and don't plan to do so--you may be better off using the community-supported version of RHEL, CentOS. It's 100% binary compatible, built directly from the source Red Hat must provide per the GPL.