Everything is OK by now !
Previously in
About 10 y/o hardware, rebuilt process :
The SSD Crucial P3 was mounted but not recognised in Bios.
Tried an another SSD, a Samsung 980, no sign of life in Bios.
Tried the P3 in an external SSD case on my main rig, recognised, but needed a format.
> The P3 is working, not DOA
Downloaded a version of Win 10 on MS site.
Tried to install with the P3 on the system, still not recognised.
The installer found the P3 and was able to install win 10 on it.
> 1st victory, but with the reboot, no sign of SSD.
And now I have to apologize for all the people saying : "Update the Bios !"
I've updated the Bios to the latest stable version ...
Just after the Bios install reboot, Win 10 is launched like a flower.
Damn guys, you were right !
Now, a bit of update, buy a cheap key and I'm done !
Thanks to all of you for the help !