回复：你如何断定"power supply"是好的？

The fan of the power supply still works. So I assume it is fine. I am a PC dummy. Now I do not know if it is fine or not after you asked. Could you tell me more?

The broke-down PC was built by a friend and I have another one which might be helpful to fix the bad one.

But I do not know what to do and how to do.