1)Try pressing alt f4 then pressing ok
2)Try win then type cmd then a black command line pops up then you type shutdown.exe /s /t 00
3)Unplug PC or if it's a laptop wait for it to run out of power could fix problem but at least it will be off
4)Run a trusted anti virus to make sure you haven't got a virus
5)Check for updates as there could be a bug fix for it
6)Last if all else does not work then reinstall windows if it does not have a virus then you can keep
Hope you fix the problem