How can the domain contriller be renamed without losing the active directory information?

it was not so clear in your description... Did you mean the server name is shown as "SERVERNAME." or "SERVERNAME.DOMAINNAME.COM."? If it is "SERVERNAME." only, I have to doubt that AD has not been installed in this computer so there is no DC in the network. But it sounds impossible to be the case since this was an upgading from a PDC and you did not mention that users in the network could not login into the domain after upgrading.

your DC name is "."? or you meant your DC name is "servername."?  in either case, you'll have to demote it in order to change its name.  Probably the "Change primary DNS suffix when domain membership changes" (right click My Computer > Network Identification tab > Properties > More) is unchecked before it was promoted to DC.  Sorry, but basically you're screwed.  The only way to change the name without loosing AD information is to bring up another DC, demote this one, change its name, and promote it back.  Backup/restore of the System State won't work either because the server has to have the same name in order to restore System State data.

Try to add an "A" record in the correct zone in DNS with this DC's correct FQDN (name) and try to promote another DC.

Good luck.

matt023 and hnminh
 -- the name of server, as shown in the computer properties is demon.lhr and the domain name is demon.isb. I have already tried all of your suggestions. It is a Main domain Controller and people are logging into the domain... but they specify the domain as "isb" not as "demon.isb" As I wrote earlier, it is not possible to bring up another DC since the process fails while trying to transfer the AD data. The error I get is " domain controller could not be contacted". Actually it is confused between the names. Initially, while trying to transfer AD data' it accepts the domain name as "isb" and later in the process it prompts that domin "isb" actually point towards "demon.isb" ; "did you mean that? ". And after a few seconds gives the error that DC could not be contacted.

I have played alot with DNS as well but all invain.

So NETBIOS domain name is ISB and NETBIOS server name is DEMON.LHR . The dot within the server name might confuse other W2K DC which part was domain name (LHR.DEMON.ISB or DEMON.ISB only). You might want to try to bring up another WINNT 4.0 BDC, which only work with NETBIOS name, upgrade it to W2K, demote the DEMON.LHR DC, choose a proper name for it and promote it back to ADDC.

To do this your AD must be running in mix-mode. Before run WINNT 4.0 setup, use srvmgr to manually add the chosen server name for this BDC as NT DBC in the domain.

this can be made to work, but you'll have to be clear in describing the FQDN of this DC.  Is the FQDN of this DC demon.lhr.demon.isb?  or the FQDN is demon.lhr?  (Type net config rdr to find out)

if the FQDN is demon.lhr.demon.isb, do the following:
-- look at the demon.isb zone in DNS and see how this DC registered its RR's
-- add an "A" record of demon.lhr in the demon.isb zone
-- change all RR references and SRV records in all sub-zone (_msdcs, _sites, _tcp, _udp) of demon.isb to point to demon.lhr.demon.isb
-- change the PTR record to point to demon.lhr.demon.isb
-- try to promote an additional DC
-- when prompted for a domain to join, specify domain.isb
-- see if this works out
-- if it works, demote the "bad" DC, rename, and join it back
-- you then should go see your friend and smack him on the head

if the FQDN is demon.lhr, you'll be in more trouble because your valid domain name is actually lhr.  You'll need to create a zone called "lhr" and allow the DC to register its DNS RR's.  your clients in demon.isb will then no longer be able to find a DC to logon to.  a domain rejoin will then need to be done for all clients.

good luck.