I didn't try another PSU, I don't have another one yet. But I had to buy another one for a pc so I will try it, I'll come back when I have it.
My ram is ok, i used it on my main pc with this motherboard and it worked just fine. I saw the code meanings but the "PCH Initialisation" is too cryptic for me.
If you have another test to ensure if it is RAM related, I would be glad to try.
By the way, the ram can be configured with XMP, is there any incompatibilities between XMP and non-K processors ?
Furthermore, the motherboard was used previously with an i7 6700K. Could it be remaining data or parameters from this processor even after a Clear CMOS ?
Thanks for all of your answers !