Acer TravelMate 7720G, Wistron Columbia 06236-1N, changed GPU but reebots randomly

Hello colleagues,
someone brought to me this machine, telling me that it had a problem with graphic artifatcs and to change the MXM video card.
As soon as I looked at the GPU code (M74-M 216RMAKA14FG) I understood that it was time to change it but I made only one heatup test to verify that the problem was really it.
Indeed, after heating the GPU, windows 10 started good and it was stable with no artifacts, so I ordered a new GPU and soldered it onto the board.
Now the problem is that the machine starts but it reboots randomly, graphics are working good in the bios and even in windows, but it doesn't matter if you go into bios, or windows or the boot options (F12), randomly this machine reboots, it doesn't shut down but acually restarts as if the "reset" button in a desktop pc was pressed.
The chassis has no signs of dents, scratches or hits, and I've found no liquid traces on the pcb, so the board is like new.

I've searched some infos on the web and have seen that often this platform Columbia suffers of these reboots behaviour, but I haven't found one unambiguous solution, someone says that it's due to the LAN IC, someone to the KBC someone else points at the southbridge, and some other to the north bridge.
I've unsoldered the LAN IC, but still the behaviour is the same...
Before going into the rabbit hole, is there any colleague that has defeated this problem with a (almost) secure solution?
Do you want me to make some voltage or resistances measures (even if I didn't find any strange or too low value around)?

Thank you for your time

Mobotool napisał(a):after heating the GPU, windows 10 started good and it was stable with no artifacts

Hello!
The auto - restart problem may be related to the GPU chip. Solder the old GPU chip back to the board, and check if the machine still auto - restarts.

Hello Matic!
Thank you for the quick answer
Actually I shorted the tale, but I already did it because I had laying around an old 216RMAKA14FGX GPU that was already reballed by me on SnPb maybe some years ago, so firstly I unsoldered the old GPU and soldered the "FGX" one but it didn't work , maybe because it was already ko (laptop started from power button but had black screen), so I put back the original GPU and made more extensive tests, keeping the laptop in windows for more minutes than before, and then I've seen that it rebooted at random times, it can stay on for 30 minutes and then reboot, or other times only just 10 seconds, so I thought that it was time to buy a new GPU.
It was not easy to find a new 216RMAKA14FG but I bought from a reliable center in Bydgoszcz (Poland), reballed on SnPb balls and soldered onto the VGA board, and it started again rebooting with the same random times, so now I think that something else is wrong.

I've tried just one minute ago the same ATI VGA board with the new GPU in another Acer Aspire laptop and it works good without reboots or artifacts, so I can be 99% sure that the problem isn't in the graphic board....and maybe it was already liked this before, maybe it was only a lucky combo that the first time that I heated the original GPU the system stayed up for many minutes that I was too fast to conclude that the problem was the GPU, basing also on the fact that I changed many GPU with the same code in the past (mainly on iMac).

Test the machine with the power button board disconnected to rule out a possible power button failure.
If it does not change anything, start with the easier things - try with a different CPU and RAM memory, reflash the BIOS chip.