Windows automatically starts a screen saver after a PC has been idle for a specified amount of minutes. This screen saver can be password protected, effectively locking the PC until a user provides her password. You can use Group Policy to enforce this setting for all users on a computer. Users won't be able to disable the automatic locking. In addition, the computer will automatically lock after the specified amount of minutes -- even if users select "None" as their screen saver. Group Policy is an advanced feature for system administrators; the Group Policy Editor isn't included in home editions of Windows.
Click "Start." Type "Gpedit.msc" into the search box at the bottom of the Start menu. Press "Enter."
Click "Yes" in the User Account Control prompt window, if one appears.
Navigate to the "User Configuration\Administrative Templates\Control Panel\Personalization" folder in the left pane of the Group Policy window.
Double-click the "Password Protect the Screen Saver" setting in the right pane of the Group Policy Editor window.
Click "Enabled." Click "OK."
Double-click the "Screen Saver Timeout" setting in the right pane.
Type the number of seconds you want to lock the PC after into the "Seconds" box. For example, type "600" if you want to lock the PC after 10 minutes.