Hello again @annaliesep ,
Believe it or not, but since my last message, I think I finally managed to pinpoint the issue -- and solve it, thanks to a lot of googling and a little bit of luck!
At first I saw some people on the web saying that they managed to solve their issue by downgrading their BIOS version (I was using the latest version from the ASUS website, namely 306). It ended up not working for me, but it sort of helped leading me to the real cause.
In the end, it seems that this whole thing is related to the computer sound system: hardware issue, driver issue (like a bad install), its hard to say the exact cause, but it seems to be the culprit! Didn't you happen to have issues with your sound from time to time, like the sound stopping to work, or you plugging earphones but them not working, etc?
In any case, there's at least a very simple way to check if that the source of the issue: completely turn of your computer, and boot into the BIOS (to do so, press and hold the F2 key while the computer is off, and then press the power button while still holding F2). Once you're in the BIOS menu, go into "Advanced Mode" (by pressing F7), then use the left and right arrow keys to reach the "Security" Tab. Then, use the up and down arrow keys to enter into the "I/O Interface Security" option, and while in there change the settings of "HD Audio interface" from "Unlock" to "Lock": this will (temporarily) disable your laptop sound entirely. Now go to the "Save & Exit" tab and... save and exit :-)
Try to then boot the computer and see if this solves the overall booting issue for you; if it does, we can move on to a more permanent fix -- where you still have your sound enabled!
Good luck!