Windows 8.1 stuck "restarting" after automatic download. No key works, can't even turn it off.

[PAT 123]

Help, please. Windows 8.1 downloaded automatically and is now stuck for the past 4 hours in "restarting". No key works and I can't even turn the laptop off. Thanks for any help you can give.

 

[Saga Lout]

If pressing the power button and holding it down for eight seconds doesn't turn the machine off, remove the power cable and the battery - that'll do it.

I shudder to think what might happen when you turn it back on. You may need a Windows 8 DVD to start afresh.