SQL Server 2008 R2 not connect to server

SQL Server 2008 R2 not connect to server

I have installed the SQL server 2008 R2 on windows 7, when i want to
connect database engine it give the following error message
![enter image description here][1]TITLE: Connect to Server Cannot connect
to (local). 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+SQL+Server&EvtSrc=MSSQLServer&EvtID=2&LinkId=20476
i tried both window and sql authentication but no success. please help.