Any way to test the individual items in another PC to see if they are working in the first place?
Start from the bottom up.
Check that CPU is fully in, with cooler properly mounted, using thermal paste. Does its fan spin?
Does the powersupply fan spin? Right voltage?
Mobo, graphics, 1 stick of memory. Does it boot into BIOS?
Swap graphics, then memory if not.
Add 1 item at the time. And so on...