The "Shutdown" button may not be available in the Start menu and grayed out when you press Ctrl+Alt+Del.
To resolve the issue, perform the following:
Click Start, Run.
Type gpedit.msc and click OK.
Navigate to the following path:
User Configuration\Administrative Templates\Start Menu and Taskbar
Double-click "Remove and Prevent Access to the Shut Down command"
Select "Not configured" or "Disabled"
Close Group Policy window.