I have two rigs (the first two I've ever built myself) both with the capacity to run 6 gpus, but when I try and add a 5th gpu the miners just don't work.

Both rigs have asus z270-a prime motherboards.

1 has 1200w psi the other has 1300w psu

I am mining ethereum on windows 10 using Claymore.

All the gpus are connected using risers, and all the risers work individually

The first rig runs 4 EVGA geforce gtx 1070s. I tried adding a 5th of the exact same card and it did not work. Also tried adding different gpus and they did not work. When a fifth card is added the system seems to boot properly but then only 3 cards are recognized, both in the device drivers and in claymore.

The second has various cards. There are 3 1070s and 2 AMD 580s. It will run any combination of 4 of these cards but I get a black screen on startup and then it eventually turns off.

Ive looked into this issue a lot but can't seem to find a way to fix it. I've heard there are issues with adding a sixth card sometimes but I can't even get a fifth.

Any help would be greatly appreciated!

This is my first home made mining rig built primarily for Eth.

I am trying to run 5 EVGA Geforce GTX 1070's, but for some reason the rig hates when I hate the 5th.  It runs 4 no problem, hashing at about 120 Mh/s (overclocked). When I plug the 5th in and turn it on only 3 come up as plugged in and sometimes gives a CUDA error in Claymore and all but crashes the rig.

At first I thought it was a riser issue, but if I just unplug any one of them from the mobo it will run 4 GPU's no problem.

Thought maybe the PSU wasn't enough even though I have 1200w so I tried using 2 PSU's, a 750w one just for one card and 4 on the 1200w. This changed absolutely nothing and it still read only 3.

PSU is EVGA 1200w Platinum
Mother board is Asus Prime Z270-A
8gb of RAM
Running on Windows 10

Any help would be greatly appreciated. Thank you.