I got this problem many times from my old computers.
Major part of the times the power supply become fail or inflated capacitors on the motherboard.
I have already get some luck too by removing all pc cards and the cpu.
After have removing all I try to power on the pc without devices and I do a bios reset and after I replace only the cpu and the memory.
If it boot I replace all other devices.
If you have a other power supply it is always good to test this first.
One of the most basic problem too is the motherboad battery...
It make one hesitate to spent few thousands dollar on a PC.
Yes I understand you.
My brother asking me to build him a computer setup similar to my current setup.
My current setup is close to 2 years old and when I have finish to build my brother computer I have seen the price is around 600-700$ higher of what I have pay 2 years before.
It's not the best time for buy a new computer with all problems from this pandemic time.
I wishes the best for you and all users in this bad times it's nothing easy.