Kyle Lahmon :
Ambular :
But the system worked/works without a GPU installed? Or have you got a different one you can try?
I have the Eyefinity Radeon HD 6570 in my system right now and it works fine
Okay, the RX-460 requires at least a 350 watt power supply, so it makes sense it wouldn't work properly with only a 300 watt. The 420 ought to be enough, though, unless it's putting out inadequate power on the 12-volt rail. What make and model is the 420-watt?
You might want to try a GTX 750Ti. It pulls less power than either of those first two I linked you.
https://www.amazon.com/EVGA-GeForce-750Ti-Graphics-02G-P4-3753-KR/dp/B00IDG3IDO
It definitely shouldn't be the PCI-E 2.0 that's causing the issue, though, unless the slot is damaged or malfunctioning.
ETA: Should have asked, did you install the correct drivers for the 460?