@Fabs, un gars qui a eu exactement le meme pb. Sachant que tous les composants marchaient séparement par ailleurs. La MAJ a fixé son pb :
"I received the Boot Kit from AMD and was able to use it to POST with on onboard video. The BIOS on the replacement motherboard, which MSI sent to me after I sent in my original motherboard with the express intent and expectation that they were going to update the BIOS for a later one that is compatible with 2nd Gen Ryzen CPUs, was E7A32AMS.190 and dated 9/20/2017. Apparently the person
AT MSI who claimed the replacement board would have the latest BIOS and that I should spend more time checking my other components was dead wrong.
I downloaded the latest one and flashed the motherboard with it, then I reinstalled my Ryzen 7 2700 and GTX1060 GPU and it worked.
(It's slow to boot considering the OS is loaded onto an NVMe SSD in the #2 M.2 slot. I disabled all the other boot devices and tried some other BIOS settings but it's still pretty slow. I saw some other threads on here about the problem and it sounds like a future BIOS update may fix it. I may try the other M.2 slot in case it matters.
merci for the help and interest!"
Source : https://forum-en.msi.com/index.php?topic=307847.0
Pour info le gars avait fait une RMA et MSI lui avait renvoyé une CM avec un bios pas à jour ! Un comble