Answers

If the IP address of a Windows Server 2012 Essentials is changed after setup then DNS lookup problems may results. To correct the DNS setting follow:

Start server manager

1. Go to tools and then DNS
2. Click on actions and select properties
3. On the forwarders tab, click on the server DNS name
4. Correct the IP address etc.

http://technet.microsoft.com/en-us/library/cc754941.aspx

http://technet.microsoft.com/en-us/library/cc754941.aspx