I have a very small (5 users) network with 1 domain controller. The domain contoller failed. I reinstalled the OS on a temporary computer and promoted it to domain controller on the same domain. Not a good idea! I finally got the 5 computers added to the domain and copied the old local profiles so the users would not scream at me so everything is fine now except the following:
I have replaced the motherboard in the original DC and have demoted it, but how can I add it to the domain with a DC that has the same Windows 2000 Product ID key? Will it work to add it to the domain and then promote it to DC when the active DC has the same license? Or how can I keep from losing all the user profiles again?
The Product ID Key will be irrelevant. If you reinstalled the old damaged DC, then using DCPromo and promoting it to be a DC in the new domain will work fine. You will not lose the user data as the this is a normal operation. The reason that you lost the user profiles is really that the user SIDs changed and the security and pointers to the profiles are based on the SID not the usernames. Each SID has a component that is based on the domain's SID that it was created in. The way you built the new machine ended up creating a new domain SID and thus resulted in new SIDs for all of the groups and users. Using a tool like ADMT and the feature from Windows called SID History you can migrate users from one domain to another.