Windows authentication problem (urgent)

Dear Everyone,

I am running Sharepoint 2013) on SQL

2008 with Windows 2008 server.I am new on sharepointand I got a strange authentication problem.

when I try to connect it using http://myservername  windows authentication works without even asking for user credentials. I have another host record on DNS server that links the same server but, when I try to connect thrught that link it it asks for windows authentication and fails even I enter credentials correctly. I have googled it but doesn't find any useful resources. how can I solve this problem? 

Thanks