Please Help me!!!!

Im have one Motherboard gigabyte 790A-DS3P and two sapphiore RX470 OC of 4gb
im using windows 10! with one cards all works fine
im put  the 2nd video card! all is ok
the pc recognize the 2 video cards
And when starting the claymore's the pc shutdown
what im need to do ?

In this vídeo of youtube this People use without problem
https://www.youtube.com/shared?ci=LGj1mF8gdHI

Im crazy ! see my topic
https://bitcointalk.org/index.php?topic=1713161.0

thanks
Almir