It’s a simple thing , but did you check that the TCP/IP configuration is correct? It almost looks like a subnet mask is wrong on the systems. The next thing is to check that the servers are actually domain controllers. If you rebuilt the first system and it wasn’t completely a domain controller prior to the second system being built, you could have this type of issue. The systems would not be part of a real domain. Check to see that the SYSVOL share has been created on the first domain controller. You can also check the FRS event log to see that the Replication Service is no longer preventing this system from being a domain controller. You may need to reboot the first domain controller to kick it into action. Once you get the first domain controller fully into domain controller operation, I would demote and promote the second domain controller to make sure the process completes properly.
If you have not applied any service pack you could do a repair on the first domain controller to make sure that all of the files are back in place. This would help with the Help File missing – and anything else that might be missing. Then apply all of the service packs and patches. Don’t forget to do the same SP’s and patches on the second domain controller immediately after the first one is completed and operational again.