How to fix laptop turning on after shutdown?

Question

Electronics

Actually the trouble itself:
There is a laptop HP Probook 640 (RAM 12GB, SSD 120GB + HDD 1TB)
Ubuntu 14.04.3 is running on it, everything is the latest from the stable.
When you turn it off in any way (except for pulling out the battery and the PSU power cord), this bastard automatically turns on after about 1-2 seconds.
Tips like "Turn off WoL" and "Cut off the network card in general" do not work. Already experienced.
BIOS has not been updated.

Answer 1

Problem solved!
In BIOS, I disabled "Wake On USB", and my wireless mouse is constantly connected.

Answer 2

Boot from any external media and check the shutdown of the job. If it still turns on spontaneously, then update the BIOS, change the system battery, i.e. fix the motherboard.

Answer 3

I assume that your power button will sink, and to refute or verify this assumption, try going into the BIOS and turning it off from there, so you will understand that the problem is in the button or in the OS