Hi @Mohammad Qasim ,
According to your description, you seem to be trying to connect to the database locally. If this is the case, I think the most likely reason is that the Sqlserver service is not started or is not running as other community member mentioned.
You could try to use
window + R and type
services.msc to view the status of Windows services, and find
SQL SERVER with instance name. It is usually Sql Server (MSSQLSERVER). Start/Restart it will be ok.
This problem may also be caused by other reasons, you could also refer to this similar case below to see more related solutions:
“Cannot Connect to Server - A network-related or instance-specific error”?
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