5090 FE - Display Glitches and screen blackout in mins after installing drivers

I have been pulling my hair out about this for the last three days. I recently got a 5090 FE and decided to build it in a Lian Li A4 H2O case. Had a lot of issues with garbled screen and sudden display blackout and assumed it was all because I got a faulty riser cable.

But after buying a new case, and installing the 5090 in my old PC without a riser (a 12100F with DDR4) - I seem to have zeroed down the issue.

I did a 5 hour non-stop YouTube test of the PC with no drivers after a DDU cleanup and it ran fine. After that as soon as I installed the driver, with a min the display went corrupt for a few seconds (small 20px by 20 px glitchy squares evenly distributed over my display) and then went completely black. And then no display even in BIOS thereafter. Letting the PC rest for a few mins resets this but reappears a few mins after use. This all in windows and browsing - haven;t even gotten to playing a single game or benchmark on it.

Here is what all I have tried.
- Built the PC with two different motherboards (An intel 12100F with a B660M and a 7600x with a B850i)
- I am using a SF1000 PSU with 12VHPWR to two 6-pin PCIe cable from the Corsair
- With and without riser cable
- Clean install of Windows
- Multiple different driver versions

Please do let me know if there is a fix or if I have gotten a faulty GPU and need to return it. Waiting for the rest of the parts to come, has made me already beyond the return window.