specifically the 'el5' bit means you are running V5 of RedHat enterprise Linux. This requires a paid support subscription from RH to get updates and support.
To check the exact version, use
then phone RH with the hostname and version details unless you already know how to login to RHN (RedHat Network).
They'll ask if you have the subscription num or 'license' num from the orig install media box.
They should be able to id your RHN acct and tell you who is the official owner/contact.