خطای A network-related or instance-specific error ارتباط با SQL

با سلام ، من بدون مشکل برنامه sql 2014 رو نصب کردم و دفعه اول وارد شدم اما برای ورود دوباره با پیغام خطا مواجه شدم ، برنامه رو پاک و دوباره نصب کردم اما باز همان پیغام خطا رو داره ، کسی میدونه مشکل کجاست؟

TITLE: Connect to Server

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Cannot connect to ..

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ADDITIONAL INFORMATION:

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)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&EvtSrc=MSSQLServer&EvtID=2&LinkId=20476

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The system cannot find the file specified

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BUTTONS:

OK

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