Installed a new GPU, now PC wont start/loss of power

[VSK933]

Hello
I have a 850w psu, b450 tomahawk mobo, 16gb ram, ryzen 7 5800x cpu and have swapped my 3070ti out for a 7900 xtx.

I ran DDU, swapped the cards and installed amd drivers and played a game for about 15 minutes and then the pc went black, started constantly turning on and off and after I held the power button down now if I turn it on the mouse, keyboard and display don't work or light up at all. The only things that work are fans, cpu cooler, gpu lights and the only thing I can see different is 1 fan has stopped spinning.

Any help welcome thanks

 

[VSK933]

What is the exact make and model of PSU?

Seasonic focus 850w gx 850

 

[VSK933]

Have you still got the 3070ti and if so does that work?

Are you using a anti-sag bracket?

Are you using 3 seperate power cables for the GPU?

I haven't had chance to plug the old GPU back in.

The 7900 came with a rod and l bracket style bracket which I have installed with the base resting on the bottom of the case and the arm supporting the gpu but not touching the fans.

I pressed the power button this morning and it tried to boot a few times then power came on with a black screen saying the memory overclock has failed but I haven't done anything further with it.

To my knowledge the ram isn't overclocked so not sure what to do with it