Vega is a very power hungry card. Though i wouldn't rule it out. Your system as is draws a good bit of power. It would still boot; 750w is the card's peak wattage if i remember properly.

Have you ...

I've just looked on the manufacturer's website and it states the GPU power consumption is 750w. With me only having an extra 100w capacity on top of that, could that be the issue?

if you take the new GPU out of the equation and the pc works fine but you then fit it and the pc no longer works its the GPU at fault

The website recommends a 850w psu which is what I have, but I'm ...

When I unplug the GPU from the PSU and turn my PC on the side lights on the GPU turn on but does nothing else because it has no power other than what the MB is supplying it.

I've just changed my GPU to from a Gtx 970 to a radeon rx Vega 64. Now when I plug the GPU into the PSU my PC will not boot even though there is power to the motherboard. If I unplug the PSU from my ...