I own a MacBook Pro from 2012 that pops a gray scren everytime I try to boot.
When I try to boot from my original disk, the screen is gray with a question mark folder. I tried Internet recovery and it seems to work out. When the loading bar is full, a screen with Apple logo appears for like 10 seconds, and then a blank grey screen, nothing happens even if I wait for a while.
I then tried to boot on Linux mint with a live key to test the hardware, it fails to install, and the screen remains blank for a while as well, same for any other Linux distribution.
Lastly, I tried to boot from a High Sierra disk that I created using a friends MacBook. The screen asks me to install it, I do so, and after about 80% of the loading bar, the screen turns grey again...
It does look like a hardware problem, but I can't manage to load hardware test by holding down
What is the reason for this behaviour? How can I resolve this issue?