Way 1: Lock computer via the user icon in Start Menu.
Open Start Menu, click the user icon and choose Lock in the list.
Way 2: Lock computer through Ctrl+Alt+Del options.
Press Ctrl, Alt and Del at the same time, and then select Lock from the options.
Way 3: Lock computer in Screen Saver Settings.
Step 1: Type lock computer in the search box on taskbar and choose Lock the computer when I leave it alone for a period of time.
Step 2: In the Screen Saver Settings dialog, choose On resume, display logon screen and hit OK.
i hope this will help u..