You can shut down or restart Windows 8 Consumer Preview by any of these options:
From any screen -> Press Windows logo key+I -> Click the Settings charm -> Click Power -> Choose which option you want.
From the Start screen -> Click your account picture in the upper-right corner -> Click Sign out -> At the sign-in screen -> Click the Power icon in the lower-right corner.
Press Ctrl+Alt+Del -> Click the Power button in the lower-right corner -> Choose which option you want.
You can also change the power options so that Windows shuts down properly when you press the Power button on the device or close its lid.
On the Start screen, type Control Panel, and then click Control Panel.
Click System and Security, and then under Power Options, click Change what the power buttons do.
Set the appropriate option for Shut down.