Thats how I started this, put 1 card in and installed everything needed then turned off and plugged in the other 3 cards. Do you have a card in the x16 slot? I'm not going to put the card onto the board I have an x16 -> x16 riser that I can use
No, I do not have a single 16x- 16x or gpu mounted directly to a motherboard. you have some other issue.