PC won’t post after looking at guide

[HOW13]

Hey guys I’m building a new PC with a 3080ti, and a ryzen 9 7900x, and a 850w be quiet pure power PSU, I’ve installed everything up until the part to test the build outside of case. 2 out of 3 fans will spin on the GPU for about two seconds before everything powers back off. No RGB occurs. It’ll just do the same thing each time I turn on and off the power supply. Yes the power supply isn’t dead I used the paper clip trick on the 4,5 connectors. Could you guys lead me in the right direction please. 

[Tridefender]

Replace GPU, not all fans came to life is worrying.