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 !

Change password on first login prompt

If you keep seeing "You should change your password on your first login etc",
In order to resolve this issue you can change the security layer of the server.

To do that Run
tsconfig.msc (Terminal Server Config)
Open RDP - TCp config page
In General Tab, lower the Secrutiy layer to RDP Security Layer
Save settings.


Now you can see the change password screen on logon.


Source:
http://www.sanderstechnology.com/2012/changing-the-remote-desktop-security-layer/10998/#.T308sUJnGQc
http://social.technet.microsoft.com/Forums/en-US/winserverTS/thread/5872fd0c-9602-41bb-8b29-3d449bb29e46/