PC won't turn on with RX 580 installed?

[etcetera4869]

Here's my PC specification:

PSU: Corsair RM850x
MB: MSI Z170A Gaming M3
CPU: i5-6600k
RAM: 2x8GB DDR4
GPU#1: MSI 1080 Ti Gaming X
GPU#2: MSI RX 580 8GB Gaming X

The GPU#2 is connected via riser, separated from GPU#1 to keep temps low.

MB BIOS are up-to-date.

Heres what happened:

The GPU#1 were not overclocked, underclocked, or BIOS modded in any way.

The GPU#2 were not overclocked or underclocked. However, it was BIOS modded (the timings, hynix memory, yadda yadda). I also used the AMD "Blockhcain Compute" driver:
https://support.amd.com/en-us/kb-articles/Pages/Radeon-Software-Crimson-ReLive-Edition-Beta-for-Blockchain-Compute-Release-Notes.aspx

I mined using Nicehash, with GPU#1 running Equihash or Lyra2REv2 and GPU#2 running DaggerDecred or DaggerSia most of the time.

Everything was fine. Both temps were about 70 C, fans were about 30%. Mined 24/7 for about 3 weeks.

However, then suddenly my PC died and won't turn on.

Interestingly enough, when I removed both of the GPU, the PC boots up into windows normally. Looks like this: http://imgur.com/a/h2Lrs

Plugged in GPU#1, works fine.

However, when I try to plug in GPU#2, either into the upper slot of the motherboard, lower slot of the motherboard, or even using the riser, it turned on for like a split second: http://imgur.com/a/Z57JY

And that's it. It won't turn on. I can't even get into BIOS/UEFI. The RAM is blinking like when it's on standby mode. Everything else does not turn on.

Could you help me? What should I do?

 

[etcetera4869]

Update: Upon further testing, I noticed that the PC can't power the GPU#2 (even if its not plugged to the PCIe slot). Only by connecting the cable from PSU to the GPU#2, that this PC can't turn on. GPU#1 is 100% fine.