Quote from: Marekkon5 on November 09, 2017, 08:44:10 PM

Hello, I have 3 r9 280x (Gigabyte).
- One is in case, in PCIe x16 Slot working fine

For the other two I have 2 expanders, and two slots (PCIe x16 and PCIe x1).
Because the GPUs wont fit inside and it would be overheating both must be on expanders outside case.

I tried all combinations of plugging those cards in those slots but none work as intended.

- Either only card nr.1 worked (0 - Internal, 1 - 1st external (PCIe Expander 0006), 2 - 2nd external (PCIe Expander 0007s))
- Or all showed up but system completly froze. (Only force restart helped)

Each time I swapped, it did one of those.

What can be causing the problem?
Too weak PSU (EVGA 850B, those cards have 300W TDP Each), or
Cable, expanders, or something else?

Well, seems you know that already, I bet you'd do some troubleshooting and tests, replaced higher PSU rating, and replace risers?

post your results, we have to do basics, then lets see on the higher levels.