Start on the Windows 8 desktop, or in a new folder - anywhere except in the Start Menu folder!
Right-click, New, Shortcut. Paste the instruction:
C:\windows\system32\shutdown /s /t 20
(remember the space between t and 20)
Name the shortcut, e.g. Shutdown computer
Use Windows Explorer to navigate to the crucial folder:
C:\ProgramData\Microsoft\Windows\Start Menu\Programs
Paste your shortcut. (In passing you can see it's not possible to create a new shortcut here)
It's reassuring to see your shortcut amongst the other Apps.
Return to the Metro UI start screen - Windows Key is the quickest way.
Tab to your shutdown tile, press enter.
Thanks Tom:
http://superuser.com/questions/408015/how-to-reboot-shutdown-windows-8-without-the-mouse