This might be a problem that power manager utilities could solve.
First install pm-utils:
sudo apt install pm-utils
Then issue the following command:
sudo pm-suspend
Your screen should display nothing. Check to see if pressing any key will awaken your computer. On my old laptop I had to press the power button to get out of suspend. If you get out of suspend, then issue the following command:
sudo poweroff
This should shut down your computer. On one of my machines where I use this command almost exclusively to shut down, I had to look at and change my BIOS configuration to allow a shut down without getting a reboot within 6 to 8 seconds after shutting down.
Good luck Lebedew.