Hi again!!
I've run into the same issue. changed CPU for G4400 and pc won't start!
If I connect only CPU and fan plus GPU,they start to run their fans automatically when switching on the power unit. But as soon as I connect one more cable (CPU power cable), it won't do anything,and when I try to start CPU it won't connect. What can it be??? What is it the most common issue or something that I might be missing??
You shouldn't be putting the parts together in the first place because you can't even tell the difference because motherboard CPU sockets and the exact CPU that works in a socket, look out for bent pin in the CPU socket, if a single pin is bent there will be problem with powering on