Struggling with 5070ti: Black Screen Issues After Driver Install

I've been having a tough time with my new BNIB 5070ti graphics card. After seeing several threads about driver conflicts causing bricking and black screens, I tried two different cards of the same model just yesterday. The issue I'm facing is that my system won't post past the login screen when Nvidia drivers are installed. My build includes a Ryzen 2700x, B450F motherboard, 32GB of RAM at 3200MHz, and a Gold+ rated 850W power supply.

I've updated my BIOS and the motherboard chipset and have tried five different versions of Nvidia drivers. I've also done a clean uninstall using DDU and reinstalled multiple times. I've reseated the card and adjusted various BIOS settings, but I still can't get it to work properly. I can access the desktop without drivers, but once I install them, the screen crashes to black. If I restart, I can log in, but as soon as I enter my PIN, the display goes black again.

Interestingly, my PC works fine with an older 1080 card and even seems fine running the 5070ti with just the basic Windows drivers. I was informed that changing the PCIe version from "auto" to "2" might help, but I can't find that option in my BIOS.

I'm considering whether to return the card and, if I do, whether to go for a 4080 super (about 300 CAD more) or a 9070xt (300 CAD less). I'm really feeling stuck here, and even the tech at the shop is at a loss. Even though some comments I've received were helpful, it seems like no one has a solid solution. I doubt a fresh install will fix this. Any advice would be hugely appreciated!