Quick answer.
This is not a full answer to your question. Judging by your post, you seem to be a novice when it comes to computer building and repair techniques.
Some of the techniques often used in testing are not really comprehensive. It is not always a series of logical steps that leads to only one conclusion.
To put it another way, there are number of things that can cause a power supply to sail or not first bonds correctly. You say that you have tried three power supplies. This would strongly suggest that the problem never was the power supply to begin with. But that is not certain, it is possible to buy a brand-new power supply that fails. But it is rather unlikely.
As a general rule, for a do-it-yourself builder extra parts and suitable testing techniques are required.
In your case you need to seriously consider the failure of the motherboard. In many tutorials people will teach about how to spot physical problems on the motherboard, and that sometimes works.
This is not to brag about myself, that is not the object here. For a long time I have been a super technician and it worked on a variety of different electronic devices including personal computers. In other words, I really am a Geek.
Lacking extensive laboratory equipment, the most practical thing to do is have on hand an extra motherboard that is known to be reliable. That is the EEC way to test the functionality of the power supply. A basic motherboard seldom draws much more than 100 W of power. That is why some systems have very small power supplies. The extra power is needed to supply power to hard drives, USB devices and a large memory array. In fact, in some cases, the memory array may take as much power as the CPU does.
Faders in motherboards are not always visible. And some types of said years are not really catastrophic failures. The CPU itself is designed to protect itself from unusual conditions, especially thermal runaway. Also, if some components draw more current than they should, the power supply also has a built-in system of protecting itself from that either thermal runaway or current overrun. This is actually a feature of the power supply, not a defect.
Also, power supplies are not supposed to work with just peripherals attached. From your post it seems like you are trying to hook up the print feels directly to the power supply without the motherboard. It doesn't work that way. The power supply has to get a signal from the motherboard that it's okay to turn the power on. The paper clip trick is used by some technicians to see if the power supply will respond to the signal from the motherboard. Even so, the best tested to use a motherboard that has proven to be reliable. If a reliable motherboard cannot bring up the power supply, it strongly indicates the power supply is not working correctly. In any case, trying to test a power supply was only print feels such as hard drives, DVD drives and things like that is not the appropriate test method.
In my opinion, you need to get another motherboard just to make sure that it is a motherboard issue. Home repairs of motherboards has limited success. From my own experience I would say the possibility of repairing a motherboard at home is less than 15% of all possible cases. And even that might be a rather optimistic statement.
Unless there is more details that you have not provided, that is the best that I can do for you right now. but before you go out and buy a new motherboard, wait and see if another member say after you provide some more details about what you are doing.
