Alright, so a friend of mine gave me his R9 290 since he upgraded to a 980ti a little while ago, and I have an interesting issue with it.
When plugging it in it shows as "No cable connected" on my monitor, and I think I might know why, but I'm not sure.
I've tried different 8-pin & 6-pin connectors from my power supply with no avail. I've made sure the card is nested nicely in the PCI express slot.
I've tried flicking the little switch on it for the Legacy & UEFI bios settings with still no avail.
What I think it is, is that my power supply doesn't have enough wattage on the main rail.
I have the Corsair CX750, and it has 130W on its main rail, whereas on the minimum specs it lists minimum 150W on the main rail.
When booting up, the fans spin on the GPU, so it's getting some power.
Oh and also, my current GPU works perfectly fine in the same PCI slot, same cables, etc...