Sql – Can’t see win2k8 server by hostname, but can see it by IP

We have set up a Windows 2008 server with MS SQL 2005 (default instance), if we try to connect using the MS SQL Server Management Studio using the server hostname it is failing.

if we use localhost or it's IP it is working.

We have added the server hostname to the hosts file (C:\Windows\System32\Drivers\etc) but this didn't solve the problem (tried point to 127.0.0.1 and it's actual IP (10.10.10.15))

The IP configuration is set to point to itself as Default Gateway And DNS server.

I've found related question here:
Can’t see win2k8 server by hostname, but can see it by IP
and something similar here:
MySQL can't see Server if hosts contain both 127.0.0.1 and ::1: entries

Any suggestions are greatly appreciated.
Best Regards