Question Newly built pc won't start 99% of the time after shut down

Jun 23, 2022
I just recently got a few parts to build a pc, Component,
psu: evga g650 "new"
Mobo: Asus tuf b450 gaming "new"
Cpu: ryzen 5 3600 "used"
Ram: corsair ddr4 3200 "used"
Gpu:zotac rtx 3060 "new"
I put it together and worked great everything was running smoothly ran a few benches got good results. After about an hour I shut it down and it would not start back up again?? I immediately thought it was ram I switched ram from old pc to the new one and worked fine again, however my old pc also worked fine even using the new ram? After a shut down, it again won't start with either ram. I than tried CPU I switched cpu from old pc and it started similar with old pc the new cpu also worked fine, switched it back and again it started but after shut down it didn't. What is wrong with this pc or which part is the issue.
Starts only 1% of the time after pressing power button or made some changes, like using 1 stick of ram or removing GPU, changing CPU, all components seem to work fine when testing on the old PC.