Kinda old but I registered only to help out.

You HAVE to plug all 8+8 pins on a FTW/FTW2 1070 for it to work properly. If you try 8pin (psu) to 8+6 (vga) like you might on other cards -
 Zotacs 1070s usually work with 8+6 for example - you will get an Error 43 at the Device Manager.

If you don't have a 8 to 8+8, buy one.

Took me 3 days to figure that out, between trying different drivers, risers, PSUs, even with the adapter that comes with the 1070s in the box it doesn't work.

I've never seen this info anywhere. If you don't give it enough power/plug in the correct way, BIOS will recognize it, Windows will recognize, drivers will be installed without any problems, but Error 43 will come upon Device Manager and you won't be able to do anything with that GPU.