C # Database Connectivity issues

Recently looking at C #, this afternoon just started to touch the C # database connection, SQL Server2008, problems with network-related or instance-specific errors when establishing a connection with SQL Server. The server was not found or could not be accessed. Verify that the instance name is correct, and that SQL Server is configured to allow remote connections. (provider: Named pipe provider, ERROR:40-unable to open to SQL

Now look at the connection string:

String constr = "server=127.0.0.1;database=" + textBox1.Text.Trim () + "; uid=sa;pwd=123456;";

Note that the server here gives the local IP;

See a lot of posts and solutions, many are focused on the SQL service within the firewall, until you see a person said, server= should be the server name, then where the server name comes,

Here it is,,,,,

C # Database Connectivity issues