issue with 7 gpu rig (mb GA-Z87X-OC Force)

[andrewaka]

Hi everyone! i try to build 7gpu rig on GA-Z87X-OC Force motherboard, but have a little problem. if u look at the mb, youll see 1 black pcie16 slot. so, when i connect 6 gpu to all slots, except this one - everyting ok and the system work fine, but when i connect the last one gpu to that black pcie16, the system starts, but nothing is shown on display. judging by the indicator on mb, there are no errors and all checks are passed. what can be a problem? have someone any ideas?
http://www.gigabyte.ru/products/upload/products/3602/1442_5.jpg

[elgi76]

* The PCIEX16_2 slot will become unavailable when an expansion card is installed in the orange PCI Express x16 slot.

http://www.gigabyte.us/products/product-page.aspx?pid=4484#sp

[andrewaka]

* The PCIEX16_2 slot will become unavailable when an expansion card is installed in the orange PCI Express x16 slot.

http://www.gigabyte.us/products/product-page.aspx?pid=4484#sp

it seems to me, that if it be so, the system will work, but wouldnt recognize the card in this slot, isnt it?