Update, I got 6 cards showing.

I unplugged all PCI 1 slots and plugged it again, it's now showing right. guess is one of the riser and trouble connecting, (weird because i checked them all one by one and they were showing right, anyway i'm glad i can moove on)

In the meantime, i encounter another issue.

when i want to launch the miner, i got a Error 0xc00007b.

I had first a MSVCP140.dll missing. i looked it up and i downloaded it and placed it where it's supposed to be,
then i got a VCRUNTIME140.dll error. same here, i looked it up and corrected the error by dowloading and placing the library where it's supposed to be.
and now, i got the error 0xc00007b.

As i was typing this, i found the wonder link : https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads

Installed 2015 and 2017 and it was fixed!

Now, another issue appears :

5 out of 6 cards are actually mining. I 've got only 15.5Mh/s out of the box on 5 cards (hynix memory and i will have to find other drivers i think)

I've made some screenshots :

http://imageshack.com/a/img922/1956/FUuHwj.jpg
http://imageshack.com/a/img923/8353/8qyiKl.jpg
http://imageshack.com/a/img923/3284/7oshp6.jpg

As you can see, miner shows only 5 cards mining. Afterburner doens't show card 1 stats. the card that is not working is on the PCIE x16 slot.
any idea on what to do?