How to solve "A network-Related or Instance-specific error" ?

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How to solve A network-Related or Instance-specific error ?

Error : solution -->add new item--> data--> ado.net entity data model -->add --> generate from database --> next -->new connection -->microsoft sql server --> continue
-->server name-->use windows authentication --> select or enter database name ---> error
(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 allw remote connections.(provider : named pipes provider,error: 40 -Could not open a connection to sql server).

please help??