BootKeyboard, can't turn on PC

[RalfJahns]

Hello,

I have an old Lenovo ThinkCentre M93p, that can be switched on by pressing ALT+p (at least with a very cheap Cherry KC 1000 keyboard and the USB receiver dongle of a not so cheap Dell premier wireless keyboard).
I fail to do the same with the BootKeyboard:

#include "HID-Project.h"


void setup() {
  // Sends a clean report to the host. This is important on any Arduino type.
  BootKeyboard.begin();
}


void loop() {
    delay(8000);
    BootKeyboard.press(KEY_LEFT_ALT);
    BootKeyboard.press('p');
    delay(500);
    BootKeyboard.releaseAll();
}

The hardware I use, is a cheap Arduino Pro Micro clone from china, I installed the additional board in the Arduino IDE from here: https://raw.githubusercontent.com/sparkfun/Arduino_Boards/main/IDE_Board_Manager/package_sparkfun_index.json
The board in general is working as an USB keyboard (can send keystrokes).

Any idea, what to do to make it work?
I don't know anything about USB. I even didn't know, that there is a special "boot" keyboard (additional to a "normal" keyboard). I don't know if the USB interface behaves differently when the PC is turned off.

Regards
Ralf