1. Follow instruction from here
by looking at C:\Program Files\Microsoft SQL Server\MSSQL11.SQLEXPRESS\MSSQL\Log\ERRORLOG
It will show the cause of the error
2. For me, when I setup the SQL server, I set the security of the SQL server to accept the window authentication only.
Follow the way how to change from SIVAPRASAD S – SIVA here
by right click at the server > Properties