For this one you have many causes like a short in the PC, dead PSU and others.
When I see this I downsize the PC. All cards come out, I pull the memory and unplug the drives and see if it powers up. If it does I unplug power and add one or two parts, retest and when I find a part that doesn't work, I leave that out and continue the testing.
So there was a short circuit 2 times in my home for some reason, but my pc worked fine after that also i used it for more than an hour. I left and came back home found that my pc doesn't switches on. the cpu fan and gpu fan moves for a sec and stops and never moves.
Any help much appreciated