There is this trick to make command line accessible. I admit I have not tested it, I can't test it now. You have access to your computer, so you don't need all the steps described there. This should work:
At the (elevated) Command Prompt, replace
cmd.exe by running this command:
copy c:\windows\system32\sethc.exe c:\windows\system32\sethc_backup.exe
copy /y c:\windows\system32\cmd.exe c:\windows\system32\sethc.exe
sethc.exe is Windows High Contrast Invocation. It can be activated on login screen. With this trick you can activate
cmd.exe instead. (The first command is just to make backup in case you want to revert.)
When you are on Windows login screen, press Shift five times to launch Command Prompt (originally it should activate high contrast or so). Then you can invoke
shutdown -s -t 0.
It is insecure in a way that anyone with access to your login screen can run Command Prompt if one knows about your hack or suspects you may have done it, or by mistake, or with intention to set high contrast. However with some simple programming you should be able to create fake
sethc.exe that will completely turn off your Windows without exposing Command Prompt to everyone.
This solution probably won't be good if you use high contrast and need original