cannot connect sql server management database engine? .i amsql server 2008

=================================== Cannot connect to Swathi-PC\MSSQLSERVER. =================================== 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: SQL Network Interfaces, error: 25 - Connection string is not valid) (.Net SqlClient Data Provider) ------------------------------ For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=87&LinkId=20476 ------------------------------ Error Number: 87 Severity: 20 State: 0 ------------------------------ Program Location:    at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean break ...