I'll tip the person who solves this problem
I have one rig with a
gigabyte ud5 x79
evga 1300 watt psu
3x radeon 290
and I have one radeon 270x I want to use.
Currently I am using the usb3 pcie x1 risers for 2 of the 3 radeons and one radeon is in the pcie x16.
If I connect the radeon 270x via another pcie x1 usb3 riser the pc turns on but nothing shows up on the screen