I have a Windows 2008 R2 server with a static IP address. When you go to the domain controller for DNS you have the A record and the Pointer record with the correct IP address. Then when you can't find the server in windows explorer network, I go back to the DNS server and both A record and PTR record have changed IP address. There are only 2 people that have access to DNS server with administrator privileges and neither one of us has changed it. Any clues? By manually changing the A Record and PTR record to the proper IP address corrects the problem.