I recently bought a RX 570 for my HP Pro 3400 prebuilt. The PSU was upgraded before to Thermaltake TRS2 S (500W).
I installed the GPU in the PC, tried to turn it on, but I got no picture on the display. GPU fans were spinning.
I tried everything from disabling iGPU, clearing CMOS, playing with BIOS, changing through HDMI, DVI and display port, trying with safe mode etc.
My suspect is that the PSU, even though it's "500W", is too weak. I don't have other PC to try it.
I also tried connecting the monitor to my motherboard when the GPU was connected. There was no signal. When I removed 8 pin connector from GPU (GPU was still left in the PC), the PC booted and the display was working. Another reason to think that PSU is too weak, I guess that the GPU draws too much power?
Full specs:
The psu is a brand new thermaltake TR2 S 500W .
HP Pro 3400
CPU: Intel i5 2400 at 3.1GHz
MOBO: Foxconn 2ABF, BIOS version is 7.16, which is latest, I think.
RAM: 4GB DDR3 1333MHz
SSD: Kingston A400 240GB
(GPU: MSI RX 570 ARMOR 4GB OC edition)