I just got mine all setup last night.
Use both 4-pin slots on the motherboard.
Make sure your Windows 10 is on version 1709 and the latest CU.
In BIOS set PCI-E to Gen2
Done, I set PCI-E to Gen2.
My windows isn't updated yet, is it really important ?
Still not working
Yes, it is. The latest KB for Windows 10 1709 includes fixes for PCI lane stuff, otherwise you have to use hackflags