PSU doesn't work

Hi, I've recently replaced my PS4 slim 1 with a new PSU but it doesn't turn it on. The weirdest thing is it does nothing whenever I press the power button, if I pressed eject button about 5-7 times then it beeps but it doesn't even power the disk drive and also the beep sometimes cuts off midway through.

The reason why I said it's weird because of there is no power into the power button is, when I connect this power supply to my PS4 Slim 2 (HDMI capacitor missing PS4 Slim), everything else works normally. I actually played games on it using this power supply before I disassembled PS4 today.

I've a modified ATX Power Supply I've been using with this PS4 slim 1 over 2 years until I used the HDMI faulty PS4 Slim's one which died couple of months ago after not playing for a while for whatever reason. I can use any of the consoles with the ATX power supply.

I don't understand what's wrong.. both PS4s are working, PSU is also working. I'm so confused to figure out as I've no knowledge in electronics or these things even I have a soldering station I bought to try things out, like fixing my own things.

Any help is appreciated!

##If you have time then you can also answer my other question I asked couple of hours before this, regarding the missing HDMI capacitor (I assume it's a capacitor).

Thank you for reading, sorry if it's too long, but I believe I've said everything which is necessary for experts to figure something out. Have a wonderful day even if you cannot answer :)