Question Freshly built PC suddenly will not power on at all if GPU is connected to PSU?

[blademontane]

i5 12600k
GTX 3060 Ti
Corsair RM850e
MSI z690 Tomahawk Wifi DDR4

I built it yesterday, and was using it perfectly fine for several hours. I even ran benchmark tests and everything was operating well within range across the board. I was watching some videos some hours later and the PC suddenly lost power. I couldn't turn it on at all, even after unplugging power and back in, changing plug sockets, nothing. I eventually started taking out PSU cables to see if it would power anything on and I found that as long as my GPU isn't plugged into the PSU, it will power on. If I attempt to power it on with the GPU plugged into the PSU, nothing will happen besides an instant of power. I will then have to unplug the PSU, then unplug and plug back in the Motherboard PSU cable before it will start again, but everything runs perfectly smoothly if I do. As soon as I attempt to plug the GPU back in, nothing happens.

I tested plugging the GPU in but unplugging the CPU, but it still didn't work, which I figured would be the case because if it was a PSU power supply issue it would have not worked in the first place for several hours. I also reseated the GPU but that made no difference. The lighting on the GPU works even when the PSU isn't connected to it though so it's not like it's completely dead.

It was a used GPU but it was in working condition when I installed it, and I did not modify or overclock the GPU at all, only the CPU within safe ranges.

What should I do? I have no idea how to fix this issue and am debating just filing a return as faulty as I bought it off ebay a week ago but I'd rather ensure it is nothing else or nothing I can just fix/diagnose myself.

https://streamable.com/eq8fh2 This is a video of what happens when I attempt to start the PC with the GPU plugged into the PSU.

 

[Lutfij]

I found that as long as my GPU isn't plugged into the PSU, it will power on.
Try and source(borrow, not buy) a reliably buitl PSU similar to yours and see if that alleviates the problem. If it does, then you need to RMA the PSU.

Did you inspect all connector for anything that might be melted or burnt? I can't tell since it's too dark, does your GPU use a 12VHPWR connector?

It was a used GPU but it was in working condition when I installed it, and I did not modify or overclock the GPU at all, only the CPU within safe ranges.
You should try dropping the GPU into a known working build and see if it shows signs of life.

 

[blademontane]

Thanks guys, I'll do all that. The GPU was bought used on eBay so the original PC isn't available to me, but I do have my current PC built that I can use to try it out. The PSU in my current PC is an EVGA SuperNOVA 650 G2 80+ Gold so I don't know if that's be powerful enough to test the GPU but I'll have a look at the specs as it won't need to power many other things for the test, and I can test the new PSU with my old GPU which is a 980 TI, so a bit weaker but hopefully it'll help so see if that works or not in the new PC.

I'll probably have to do it tomorrow as I won't have enough time today but I have the day off tomorrow.

 

[blademontane]

Did you inspect all connector for anything that might be melted or burnt? I can't tell since it's too dark, does your GPU use a 12VHPWR connector?

Here's a link to a closer picture of the connector and cable. Also I can't see any damaged connections anywhere.

https://ibb.co/HtMZmZp

 

[blademontane]

I had a bit of time so I switched the GPU's between PC's and my old PC won't start at all with the new GPU, and my new PC runs fine with the old GPU.

A 3060Ti draws 200W and my old GPU 980Ti draws 250W so it can't be the PSU, so it must be the GPu.

Can anyone confirm if my logic is sound with this? I haven't dealt with these issues before as this is my second only build so I want to make sure before I return it.