Enable Ctrl Alt Delete For Vista Logon Screen

Open the Advanced User Accounts panel by typing in netplwiz into the start menu search box, and hitting enter. Then click the Advanced tab, and you’ll see this:

Just check the box, and the next time you login, you’ll see the old familiar prompt.

Update

For a method that works all the time, type in secpol.msc into the start menu search box and then navigate to Local Policies \ Security Options.

Find the setting for “Interactive Logon: Do not display last user name” and change it to enabled.