You can plug in 1 graphic card to boot up and do all the configurations then add more cards 1 by 1
This is the problem, if I boot up with one card , in the pcie1 ( the only 16 pin pcie on the motherboard , and as intruction on the motherboard says , the first one that i have to install) the computer wil start , the fans also but i have a black screen. And this happens only when i have a card plugged in this pcie1.