Why my PC not shut down completely?

This could be due to a few different reasons but this is probably due to configurations with the fast boot option in the bios, uncheck this option to ensure the pc can shutdown without restarting its previous state.

Double check your alert wake up timers and/or check the wake on LAN settings as well but check your bios settings for the option I mentioned previously that will solve the autorestart, also you could try holding the power button for a force shut-off but check the fast boot option first and then if you have issues I will assist.