Power supply wont work when connected to video card

[motoadve]

Have a HP Omen 30L gaming PC.

Wanted to upgrade the video card to a 3090Ti , which needs a bigger power supply.

Bought a Corsair RM 850X, when every thing was connected it would not power up the PC, but if I disconnect the cables that go to the video card then it powers up the PC, thinking was a bad PSU, bought another one, a RM1000X, installed it and exact same thing happened.

Re installed the old video card, thinking the video card was bad,  same symptom with the old video card, only powers up with the cables to the video card disconnected.

Any ideas what the problem might be?