Domain controller not registering as a DC

[Dos_Box]

Quick overview.
Sunday night we had a powercut and all systems shut down (UPS) as required. Power returns and all systems restart. The air-con does not. Many hours later I get into work and hear the sound of tortured server fans screaming as they blow red hot air over already over heated chipsets.
I have a small training network where I work to cover 2 rooms (40 PCs) and have (had) 2 servers running, both running as domain contollers running it, one old (to be retired this summer) and one new. The old one just turned up its toes and died. The new one already had all the FSMO roles and primary functions transferred to it, but it looks as if when the old one died they were replicating the AD database. I have recovered quite a few issues so far, but my biggest is that the remaining server does not see itself as a domain controller and netdiag fails several tests reporting the same as it looks elsewhere for a DC. Does anyone know where to find the info that will enable me to force it to recognise itself as a domain controller. My clients can still logon and use network resources, but I cannot edit GPs (it looks elsewhere) and other little (and not so little) niggles. Short of re-installing from scratch can anyone help with this?
I have removed all traces of the old DC in AD and with NTDSUTIL, so its gone. I just need to get the new one to realise what it is.

[StewartKnight]

sounds like DNS to me!

[Dos_Box]

Is a bit of everything, but all error messages report the same. LDAP, Kerberos, AD, everything simply report back that they are not going to play because a domain contoller cannot be found.

[altecsole]

How about adding a virtual machine and promoting that to a domain controller? With a bit of luck it may work and you then then try to demote and then promote your misbehaving DC? I may be talking the proverbial, so ignore me if I am.

[NetworkGeezer]

But if the problem DC is not responding as a DC then there is effectively no AD so any newly promoted DC will have nothing to replicate.

DNS is probably most promising avenue.

Also look at the directory service to see if that's up.

Firewall configs in case something is blocking off ports - long shot but worth a try.

Check for unexpecyed listners on relevant ports

Dos_Box do you have no backups whatsoever?

[altecsole]

But if the problem DC is not responding as a DC then there is effectively no AD so any newly promoted DC will have nothing to replicate.?

If users can still logon then a DC is there, but something is messed up. I just thought promoting another DC may fix the problem? If all else fails it's worth a try?