Could not open a connection to SQL Server

Today, I was trying to connect to SQL Server and I got the below message. I don’t know what went wrong I restarted my machine.

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 allow remote connections. (provider: Shared Memory Provider, error: 40 - Could not open a connection to SQL Server) (Microsoft SQL Server, Error: 2)

Solution:
I did little bit of R&D around this. What I am trying to do is using SSMS connecting to the SQL Server. SSMS is a front-end tool for SQL operations. And the error message shows that "Could not open a connection to SQL Server".
So I thought SQL Server service is not running. So I opened SQL Server Configuration wizard to see if I am right or wrong. Yes I am right. SQL Server service is stopped. I restarted the service and now everything looks fine.