[SOLVED] After attempting to install GPU, computer won't boot

[IO_OI]

I installed windows on a newly built PC using the integrated graphics before attempting to install the GPU. Windows installation was successful,, so I turned off the PC and added the GPU. The system wouldn't boot, just idled without any output from the motherboard or GPU. So I did some troubleshooting:
-Double checked connected properly
-Used different plugs to put into the GPU
-Reset the CMOS/BIOS by taking the battery out and putting it back a few minutes later.
-Tried to install the GPU driver (wouldn't install before the hardware installed)
-Updated the BIOS
-At each stage I tested the mobo HDMI port, and both the GPU HDMI ports and there was no output

As far as I can tell the issue is with the GPU, but I have no reason as to why except power of deduction. I don't have another system to test the GPU, or another GPU to test the PCIe slot. And just to reiterate, everything works perfectly without the GPU plugged in.

Any suggestions to other things to try? I'm not sure if i can prove faulty goods with only this information in order to get a replacement. I appreciate any help.

GPU: ASUS DUAL-RX580-O4G (new)
MOBO: MSI H61M-E33 (used)
PSU: Thermaltake Smart RGB 500W Power Supply (new)
CPU: Intel Core i5-2310 @2.9GHz (used)
RAM: Corsair Value Select 8GB (2x4GB) 1600MHz CL15 DDR3 (new)
SSD: Crucial BX500 2.5in SATA SSD 240GB (new)

 

[Phaaze88]

Newer gpus require motherboards equipped with a UEFI bios. Yours is Legacy only; it will never recognize an RX 580.

Because of the Legacy only bios, the most recent gpus you can plug in are:
-on Nvidia's end, GTX 700 series
-on AMD's end, Radeon R9 series

 

[IO_OI]

Newer gpus require motherboards equipped with a UEFI bios. Yours is Legacy only; it will never recognize an RX 580.

Because of the Legacy only bios, the most recent gpus you can plug in are:
-on Nvidia's end, GTX 700 series
-on AMD's end, Radeon R9 series

Thanks a heap ) Didn't manage to figure that out in all my searching.