sql server authentication login failed
Connect to SQL Server using Windows authentication. Run sp_readerrorlog and see the complete message which would have come in errorlog when you tried connecting with SQL Authentication. This message is not of much help. You can update the question with message


  From error log: Login failed for user 'sa'. Reason: An attempt to login using SQL authentication failed. Server is configured for Windows authentication only.


What is output of this query.

select serverproperty('IsIntegratedSecurityOnly') 

It seems like authentication mode is Windows only. If above query returns 1. It means authentication mode is windows go to server . Right click on SQL Server select property and then click on security. Change authentication it to mixed mode by selecting radio button SQL Server and windows authentication mode and restart SQL Server service again.