No, the power button as well as the NOVO button are on the side, on a separate board connected by a daisy chain (see pic). The response to both buttons is the same - the power button lights up for 5 seconds and then goes of...

Yes, I tried that too, unfortunately the result is the same. The only thing I remember and what I'm almost (!) sure of is that the last time it turned on after such an idle time I didn't touch the power button at all....
In fact, I would have thrown this laptop into a long box if there had not already been such a precedent with revival. Maybe there is some emergency (?) startup mode, maybe there is some way to start the motherboard without the power button.
It may be possible to short some pins on the cable from the power button board to the motherboard, but I have not been able to...

I'll tell you right away, I don't understand much about electrical engineering. I have this laptop, the symptoms are as follows: when I press the power button it lights up for about 5 seconds and then goes out. The fans do not spin, there is no effect at all.
Here is what diagnostics I was able to run:

1) The motherboard sees the battery (the button lights up white if it is connected and red if it is not, as if it is almost discharged).
2) The charging LED is also on if the battery and power supply are connected (without the battery it just flashes quickly and goes out...