need help trouble shooting a crossfire setup

current pc
z87 g41-pc mate
i5-4690k
750w psu
r9 285 2gb

got a 1440p acer monitor on sale for $200 last week. I dont game much anymore, so i decided to cheap out and get a 380 4gb for $160 instead of a single gpu setup. Was planning on selling the 285 later and getting another 380 4gb. two of them should handle anything at 1440p.

For now though, I just want to use the 285 with the 380. They're the same chipset so they should work fine together, and I understand it will only utilize 2gb of ram. each card works fine when installed on it's own in the main pci'e 3.0 x16 slot. when I try to install the second, for this mobo it's a pcie 2.0 x16 slot, I get no display output from anywhere. no hdmi, no dvi, not even anything from the pc hdmi/dvi ports. Curiously enough, i tried removing the gpu while leaving the 2 six pin power cables plugged in, and the same thing happened, no display.

any ideas?
could it just be a bad second pci slot?

eta - either card works fine in the second pci slot with nothing in the first. I'm at a loss here. The mobo was an open box special from fry's. Couldn't get the os to install properly when i first built this, I had to manually flash to an older mobo bios. could that be the problem? that wouldn't explain why the problem arises as soon as a second card is plugged into the psu but not the mobo though

recommended psu wattage for this setup was only 610 when put into a psu req calculator