Pretty much every time I’ve put a computer together I’ve had that happen
I just take it apart again and do it again and usually it fixed itself, might just be missing one of the wires plugged in like the CPU power isn’t in all the way or something
Cpu/pcie cables used properly? Pinouts on them are different and in my more inexperienced days, i used them interchangeably and got something like this. Luckily i didnt blow anything up
Mine did the same. I didnt plug in one of the fans and it would cause it to shut off. I ordered an extra 4 pin adapter to power the extra fan and done.
It's most likely something to do with you cpu power as you have your other lights on I would say try reseat your 8 pin if that fails try reseat you cpu but if that's not seated right it would power on just wouldn't post
It won’t be the psu 99.9999% of the time. I say it’s maybe a cpu power issue or faulty cpu or power delivery around the cpu. Check all the 4/8 pin connectors are in next to the cpu etc