A client problem, not server's : A network-related or instance-specific error occurred while establishing a connection to SQL Server...

I don't know, when and why, I cannot connect remote SQL server from my win7 & winserver2008 (64bit) machines. When trying to connect a server by typing IP ( xx.xx.xx.xx ) in the server name in "Management studio->Connect Server" dialog box, I always get:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 53)

or ( If typing "xx.xx.xx.xx,yyyy" - assigning port )

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 0 - TCP Provider: ) (Microsoft SQL Server, Error: -1)

Well , after cautious checking I am sure it is not caused by wrong server configuration, since I even tested onnection from another XP3 32bit computer and it's OK, implying problem lies in my win7 client.

It's really very,very weird ------ no detailed information for the error even seeking event viewer. Eventually & luckily I approach to get around it : just connect local server by type IP format server name: "127.0.0.1" ------ it is like some internal mechanism that "IP" server is triggered ; once IP is triggered locally, it could be applied on remote connection. After connecting "127.0.0.1" I could get my remote server connected.

Does anyone know why thing goes as this ?