[SOLVED] PC not powering up if I connect New GPU.

[KappuK]

Hi, I am facing a problem with PC not powering up if I connect New GPU.
Specifications:
MoBo: Gigabyte B85M-D3H (rev 1.1), Updated with recent UEFI BIOS available.
CPU:Intel Core i7-4770 CPU @ 3.40GHz, 3401 Mhz, 4 Core(s),
Windows 10 x64, updated to the latest
RAM: 32 GB
PSU: SEASONIC 750w

So far I have been working fine with onboard Intel Graphics Card. Recently I ordered a brand new Gigabyte AMD RADEON RX590 GPU. It needs external 8pin power cable but it doesn't come along with GPU. So, I ordered a power cable separately.
Now, when I place the GPU to PCIe x16 slot (I am sure it has sat properly and locked) connect the GPU power cable and switch on, PC just doesn't respond(no LED indicator, fan spinning, POST ...) . The moment I disconnect the power supply to GPU from PSU, It boots and connects to onboard graphics.
What I have tried to fix it -

1. updating BIOS to latest (2017 release from 2014 OEM release),
2. removing CMOS battery for 5+ minutes and set BIOS to defaults, etc. (Checked BIOS default is set to boot from PCIe, and it has onboard Graphics enabled)
3. tried placing GPU on PCIex4 slot

but it doesn't help, It just doesn't power up if GPU is connected to PSU. If I disconnect the power supply to GPU it boots.

I could sense it is either a power cable or GPU (or maybe PSU) issue. I do not have a secondary GPU power cable or GPU or PSU to test.
BUT am I missing anything else, (Compatibility check, SW/BIOS config, or whatever) before I order replacement hardware? What another testing I can do?

 

[bmockeg]

Your power supply should have the 8 pin power adapter needed for your GPU. If it does not have an 8 pin VGA power connector then you need a new power supply.

 

[KappuK]

Your power supply should have the 8 pin power adapter needed for your GPU. If it does not have an 8 pin VGA power connector then you need a new power supply.

My power supply has 8 pin PCIe power connecter, but unfortunately i have lost original GPU cable came with PSU. I ordered a new 8 pin power cable from Amazon, but it is not from same manufacture so not sure if it works or not.

 

[bmockeg]

My power supply has 8 pin PCIe power connecter, but unfortunately i have lost original GPU cable came with PSU. I ordered a new 8 pin power cable from Amazon, but it is not from same manufacture so not sure if it works or not.

Never do that! Different cables are wired differently. Potentially could have destroyed the GPU.

 

[KappuK]

[Solved]
It was a problem with the Graphics Power cable. Though 8-pin cable fits properly on both PSU and GPU ends, it doesn't do any job. This stops even switching-on the PC. I found a replacement cable, which works fine. So, the learning is 'with wrong PSU->PCIe cable, PC won't boot. Thanks a lot for all your help and support.