Microsoft SQL Server, Error: 18456 – Login failed for user.

If you encounter this error while connecting to the SQL Server  SQL authentication, the solution is simpe.

Connect to the server with Windows Authentication

Just check 2 things:

1. Go to Security -> Logins and right click to the user -> Properties -> Status
Login section should be Enabled

2. Right click to the Database Engine, Go to Properties -> Security 
In Server Authentication section, make sure

SQL Server and Windows Authentication Mode is selected.

It would need a SQL Server restart, which you can do by:
Start - > Run - > Services.msc

Go to SQL Server  and Restart it.

Thats all !