Question Laptop won't boot unless with PSU plugged in or pressing/keeping power button

Feb 12, 2020
Hi, to everyone.
I'll explain you my situation that is actually pretty weird. I own an Asus Rog G750JZ that had a 500gb HDD built-in, and a couple of years ago i fried it up probably because it was kind of old. So i got a new fresh 250gb Samsung SSD and the laptop was again running fine. I noticed that i needed more space (clairly) and then i bought a used 1tb Kingston SSD.

Now i'll get into the real issues with the latest one i added:
  1. The laptop with SSD unmounted, starts fine and works fine.
  2. I manage to start it with SSD mounted only if (i think so) i drain the charge inside by keep pressing for a bunch of second the power button and repressing it various times.
  3. The laptop starts fine with PSU plugged in (even with battery mounted or not), but it doesn't detect the SSD.
I used some tools to check the health of the SSD and seems like it's not on the way to breaking itself.
When i use method 2 (on the list above) the laptop runs good, but suddenly sometimes it reboots itself and it change SSD drive letter.

I also verified if it was a battery issue, and then i realized that my battery when full charged and system on full perfomance, was lasting longer just for like 30 mins. I ordered it yesterday, and i will test it in a few days when I'll receive it.

Meanwhile, if someone can explain me what could be the solution, it will save my life.
Thanks in advance!