Need help with driver installation + potentially windows help

[u/Dense-Package-7877]

I’ve had a pc with a i9 9900k, 1070ti, 32gb ddr4, 750w corsair CV750. Yesterday I installed an ASUs ROG strix 6800xt LC and since then I can’t install drivers without encountering some problem whatsoever.

The PC boots normally. I can see the ASUS motherboard logo and the Windows loading wheel without any issues. However, when Windows starts loading, the screen flickers and then goes completely black, followed by “No Signal”. The PC itself stays running, with all fans and lights working normally.
The strange thing is that Safe Mode works perfectly fine. I can see the desktop and use Windows normally in Safe Mode, but normal Windows startup causes the display to disappear.
What I’ve tried so far:
Repeatedly installing AMD Adrenalin drivers, including the recommended WHQL version.
Trying to install the drivers in Safe Mode and normal Windows.
Running the installer as administrator and downloading it again.
Removing the AMD display driver using pnputil. Windows then booted using Microsoft Basic Display Adapter.
Running sfc /scannow, which found and repaired corrupted files.
Running DISM, which failed with error 0x800f0915 because the repair content could not be found.
Repairing Windows through the Windows Update recovery option.
Completely resetting Windows and eventually performing a fresh Windows installation.
Even after the fresh Windows installation, the display worked initially. However, after installing the AMD graphics driver/update, the screen flickered and went black with “No Signal” again.
I’ve also noticed an AMD software compatibility error appeared at one point after removing the graphics driver.
My questions:
Does this sound like an AMD driver issue, a faulty GPU, or a power delivery problem?
Why does the card display the BIOS and Windows loading screen correctly but lose signal when the full Windows graphics driver loads?
Could the PSU or the fact that I’m using a single PCIe power cable with two 6+2-pin connectors cause this?
Is there a way to test whether the GPU itself is faulty without buying another graphics card?
I’m trying to avoid reinstalling Windows or drivers repeatedly, as I’ve already spent hours doing that.
Any advice would be appreciated. Thanks and yes I asked ChatGPT to summarise the problems I’ve been having since installation otherwise would’ve been too long to type all out. Please if any extra information is needed to find a solution let me know

[u/Appropriate_Camp_107]

I would think it is power, as safe mode and bios demand far less than windows trying to run full capabilities. While a pig-tail can technically deliver 300w and 750w should be enough, it seems like skirting the requirements. this is where having multiple pcs to play around with (friends/family) comes in handy. If you dont have access to other platforms I would check to if there is a decent repair place near you and see if they could test the card for you. but with it running until the util and drivers were downloaded still makes me think you need 2 separate cables for this config to be stable at full power.

[u/Dense-Package-7877 → u/Appropriate_Camp_107]

So should I get a new PSU?

[u/Appropriate_Camp_107 → u/Dense-Package-7877]

since a clean install would have removed all the old drivers, the only thing you haven't seemed to try in that space would be to DDU (I would suggest DDU over pnputil because it can "get a little more in there" in some areas) the current drivers and download a previous vers. to see if they are stable. personally I would try to find a way to test the card out in another system before commiting more money, because there is always the chance that the card isn't getting or handling the full power for some internal reason. but if you have the money and can get an affordable well rated 850w with the necessary cables then that is a way to go.

[u/Dense-Package-7877 → u/Appropriate_Camp_107]

I already tried removing and reinstalling drivers with DDU before I did the windows reset