Issues powering on Fujitsu Celsius M730n (no power at all)

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I have bought a Fujitsu Celsius M730n to build a really cheap entry-level gaming PC.
 

Here is the user manual:
https://support.ts.fujitsu.com/indexdownload.asp?Softwareguid=79a5ac8e-122d-401c-8786-edcdd526dfa8

I thought I got quite a good deal, but I am not able to get the PC working. The computer was stripped of all the RAM, hard drives and GPU. The computer also arrived with some of the inner connectors unplugged, so before starting, I plugged in what I was able to determine to be plugged in. This included the front IO connection and also a USB 3.0 port in the middle of the board. I also added a stick of ram and a GTX 960 graphics card.

The computer has a Xeon E5-1620v2 processor inside, which I checked, and I could not see any damage to it.
The motherboard is D3128-A25 GS1.
 

After the computer was not able to start at all, even after multiple checks that the power cord was connected (and tested that the socket works) and verified that it was working on other computers, and checked for all the connections in the PC. Everything seemed alright, so I tried starting the computer by shorting the red I/O pins with the same result. I also tried this with the RAM (I have only a single stick available at the moment) in multiple different slots. I also tried removing the CMOS battery, but nothing I tried helped.
 

After these steps, I unplugged everything from the case and tried the motherboard with the power supply outside of the case. With the same result.
 

I have followed the steps described in: https://linustechtips.com/topic/42440-readme-how-to-respond-to-a-no-post-or-no-power-up-situation/
 

I tried connecting a hard drive to the power supply alone and starting, I was looking for a spin from the power supply fan, but I did not notice any movement.
 

The last one was shorting the green wire to the ground on the power supply and attempting to start. Neither of these worked, and I have no available compatible parts. Therefore I am asking you for any help and suggestions as I have not previously worked with Fujitsu prebuilt systems.
 

1. Are there any common gotchas with Fujitsu motherboards? I know some manufacturers required specific parts or wire connections to the motherboard in order to start the system.

2. Is there another way to test the power supply? I, unfortunately, do not have a multimeter, and I do not have a power supply tester at hand at the moment (but since the power supply connectors are non-standard, I would probably be unable to use this in this case anyway).

3. Do you have any other suggestions I should try?

4. I also took some pictures of the connections on the motherboard. If anyone with experience with Fujitsu systems could check if I am missing any, I would be very grateful.

5. Are there any adapters which I could buy to test out the system with a normal power supply? I was unable to find these by searching my usual three for such stuff (eBay, Amazon, Aliexpress).
    

As I assumed this computer would work, I also bought some ECC memory, so I will be able to try different RAM tomorrow.

Thank you in advance for any suggestions and tips! If I forgot to include something important, please let me know, and I will try to add any information you would find helpful to solve the task.