I go the error message while trying to start MSSQLSERVER service. The detailed error message is: Windows could not start the SQL Server (MSSQLServer) service on Local Computer.
Error 1069: The service did not start due to logon failure.
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Normally you will get this error if you have changed your network password.
go to start -> run and then type services.msc this will open the Services window. Search for SQL Server (MSSQLSERVER).
Then right click on that go to properties as shown in the figure below.
This will open the Properties dialog box, Navigate to the Log On tab and change the password and shown in the figure below.
Then try starting the service it should work.