A network related or instance specific error in sql server

Question

A network-related or instance-specific error occured 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: Name Pipes Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 2)

 Please Solve My Problem

This Problem  occured again and again in my sqlserver  Please give reply to me