By default you don’t have to press Ctrl+Alt+Del when logging onto a Windows computer unless that computer is part of an Active Directory Domain and then it would most likely be running Windows 7 Professional and you would be required to use Ctrl+Alt+Del to logon
By pressing Ctrl+Alt+Del before putting in your name and password gives you an extra layer of security by preventing rouge programs that may be trying to get your login information by using key loggers or fake login screens etc from running before you log in. It brings up the Windows security screen allowing you a safe login.
To enable Ctrl+Alt+Del logins for Windows 7 computers all you need to do is click on Start and then type in netplwiz in the search box to bring up the Advanced User Accounts Control Panel tool. From there click on the Advanced tab and check the box that says Require users to press Ctrl+Alt+Delete and click OK. Just be careful when changing settings here so you don’t accidentally change something and not be able to log in!