Problem to access the SQL Server

I have SQL Server 2005 which is installed on server machine.

I was working fine on SQL server before I change the server machine IP. I changed server machine IP to host the Web Service on it.

But now when I enter the Login and Password information SQL Server displays this error message:

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: 2)

I also tried to remove Server machine IP, Still I can't able to access the SQL Server. My all database stucked in it. Or can I recover my SQL server database?