Question MSI B450 / AMD RX580 - Signal launch as soon as I launch any game or GPU test

May 25, 2020
Hello guys,
I have been struggling for two full days on this and i'm begging for any help.

I 'built' my first computer 1.5 year ago (see config below). It works smoothly for any non gaming stuff (even photo editing) and I actually never did game much on it. But now I finally had time to, and when i launch ANY game, as soon as the GPU fans start spinning, the screen loses signal. I think the whole computer is crashed (hard to say without screen, but the noise is also cutoff), the CPU and GPU fans spin quite fast and never stop until I manually force-shut down the computer. If I try any GPU testing tool (like UserbenchMark or FurMark), they detect the GPU, but as soon as I launch any test, I get the same issue (signal loss, fans spinning, computer crashed).
Note: I have no integrated GPU in my CPU and my desktop work goes smooth. I can even do photoediting in gimpshop at high resolution.

MSI Tomahawk Mortar b450
BIOS Version/Date: American Megatrends Inc. 1.00, 7/16/2018
CPU: AMD Ryzen 5 2600
Memory: 16GB GDDR5
GPU: Sapphire Radeon RX 580
VBIOS: 113-1E3870U-O49
Driver: 26.20.15019.19000
PSU: Seasonic M12 620W
OS: Windows 10 Pro x64 v1909 (OS Build 18363.836)

What I tried:
-Updated GPU drivers (using AMD Radeon Adrenalin 2020 Edition)
-Updated MSI drivers (using MSI Live Update 6)
-I tried 2 different HDMI cables
-I tried 2 different screens
-I tried to change the power limit to -30% or +30%
-I tuned the GPU to -50%
-I tuned the VRAM to its lowest possible value
-I tried launching games in 800x600 with lowest details possible
-Remove and put back the GPU
-I had issues with my Windows 10 Home which was stuck on v1803. Since everything I found on the internet didn't work for me, I thought it could be the reason, so I bought and installed a new Windows 10 Pro v1909 on another SSD. It did not fix the issue.

When monitoring the GPU with FurMark (just monitoring, as any testing causes the crash) while I do photo-editing at high resolution on gimpshop it shows the GPU utilization going up and down and everything seeming normal. Same when monitoring with Radeon Software.

I am litteraly begging for any help. Please keep in mind I am not super tech savvy :) I tried to provide all the relevant information but please let me know if I forgot anything.
Thank you so much for any help on this!