So I have three mining rigs built exactly the same way in terms of motherboards, power supplies, graphic cards etc...
Problem is one of those rigs will simply not show the 8th GPU. I've tried everything (changed risers, usb cables, power lines, graphic cards etc...) and it still wont show the 8th GPU!
It's no the GPU and it's not any of the things mentioned above so what the hell can it be?!
I've made a clone of the ssd and the bios settings are all the same across all three rigs so why is this one not showing me the last GPU?
What else can I try? I've been at it for two days now and it's becoming really frustrating!
Have you checked every section in Device Manager? Sometime I got the same problem, and the interesting thing is the last GPU was displayed not in Display, so I just right click on it and update driver for it. Then, it should be ready to mine.
Lol. As far as I know there is only one sector in the Device Manager for the GPU- and it is called Display adapters. The OP said that the other 2 rigs have everything setup the same way as this rig which does not recognize the 8th GPU.
Maybe in the device manager other areas you can see a yellow exclamation mark but that is highly unlikely since the OP said he has spent two days troubleshooting it.
Have you OP updated the BIOS to the latest version of your motherboard ?