Hello,
The easiest way to troubleshoot this issue is to simply replace the suspected bad devices with known good working ones.
You can't really troubleshoot what "part or section" of the motherboard is defective, and even if you could troubleshoot it, you probably couldn't do anything to fix that "part or section" of the motherboard, unless you had some sort of engineering skill, I guess.
With the power supply, you can test the cable that plugs into the motherboard to make sure that the power supply delivers the required voltages and provides the required resistance.
If you recently purchased the computer/motherboard/power supply, contact the manufacture to get the defective product replaced/repaired.
N