The flickering followed by a black screen sounds like the videocard. Have you tried running diagnostics? Reboot the PC and you can access by pressing F12.

"have tried re-installing drivers, repasting"

1.  Unfortunately by opening up the GPU for a repaste it voided the warranty on the OEM GPU.

2.  Check the GPU temps, including the video card VRAM, which are not monitored in AWCC.

3.  If you already have it open you could check for cracks on the GPU die and corners, most commonly this cracks from over tightening the GPU heatsink but also from overheating.  A lot of people really like to clamp it down which is bad for the die especially when it gets hot and expands thats when hairline fractures can occur.

The latest Vbios for the RTX 3000 series card has had a few people report that display compression over DisPlayPort seems to be broken and causes issue on higher refresh rate monitors when they get black screens and video card output dropouts at refresh rates of 240 Hz or higher.

If you use a high refresh rate display try lowering it to 60 Hz and see if the problem stays, or goes away.