How do I switch off the Ps4 when it has completely hung up?

My Ps4 has hung up and only shows a black screen. So I can't turn it off using the menu. However, I can't force the shutdown either, because if I press the start button for 7-9 seconds, nothing happens, it doesn't even emit a beep. Actually, that should force Ps4 to switch itself off. At the moment it lights up slowly all the time, I don't know if I should just pull the plug.

Take off the power or hold the power button down for a few seconds.

If nothing else works then you should do it.