No GPU Detected, Gigabyte Z790 Gaming X AX (Rev 2.0) (New Mobo & New GPU)

[Hypnotech03]

Hey Guys,
Quick run of specs first
Mobo: Gigabyte Z790 Gaming X AX (Rev 2.0)

CPU: Intel i7 12700K
GPU: Gigabyte RTX 4070Ti Eagle OC 12GB (running 2x 8pin to the 12vhpwr adapter)

RAM: Kingston Fury 5200 2x16GB
M.2 Storage: Samsung 980 Pro
PSU: Cooler Master 850W (MPE-8501-AFAAG)

Long story short i've upgraded MOBO & GPU in the last 48 hours for 2 reasons (old Motherboard was Asus Strix B660-F Wi-Fi, old GPU RTX 3070Ti)

1. Old Asus Strix B660-F Wi-Fi had already had a warranty repair but the PCIex16 was still faulty so my old 3070ti was running fine in the second slot
2. Started crashing and getting black screen during heavy load games. tried every possible software fix, DDU, clean drivers, old drivers, 

Upgraded the Motherboard yesterday to find even the new motherboard was not detecting the GPU, figured maybe the GPU faulty
Upgraded the GPU today to a RTX 4070ti and still no GPU detected in any slot.

I have enabled and disabled iGPU in Bios.
Changed primary display OI Slots to be both iGPU and PCiex16. still nothing.
updated bios from FB (Bios date Dec 20, 2023)to FCd (bios date Mar 22, 2024) and nothing.

Tried swapping cable ports on the PSU..

Any help greatefully appreciated

 

EDIT: after further fiddling, putting GPU in a x4 slot I get it to detect in both Bios and Device manager.

I was able to update Nvdiea drivers. But still nothing when put into Slot 1 (x16)