Disable Lock Workstation
Ctrl-Alt-Dlt Screen

Registry Settings

User Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\ System]
System Key: [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\ System]
Value Name: DisableLockWorkstation
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = disabled, 1=enabled)

 Source: http://www.winguides.com/registry/display.php/264/