Hi! I just upgraded some of my pc parts. PSU, SATA SSD, and rtx 4060

So I was using this old pc prior just fine. No gpu and it has old hdd. I decided to change the storage to ssd first, then I changed the psu from 350w to a 750w gold. But when I installed everything (psu and gpu) the cpu fans would turn on but turns off again. I also notice that the power button does not lights on like it used to when I try to turn it on. Here’s what I’ve tried so far:

1. Reinstalled the 24 pins, pci-e, as for the mobo, my mobo is an old model that uses 4 pins ATX, my new psu only comes with 4x4 pins. I searched that it can still work if I insert the 4x4 pins (only the half of it) in the 4 pins atx (I think should work as well since it clicks and fits when I insert it)

2. Tried using 1 ram only. Reinserting the ram, clean it, and swapping the slots I’m using.

3. Rechecked all cables (24 pins, etc). Removed and reinserted, still same problem.

4. I removed the gpu and the pci-e cables. Still didnt work.

Does anyone have a solution for this? Or am I doing something wrong? I’ll list down the specs of my pc.

1. Processor: intel I5-6400

2. 2x 8gb ram ddr4

3. SATA SSD 1TB

4. PSU: gigabyte ultra durable 750w v2 gold plus 80

5. Rtx 4060

ps: i checked prior before i got the parts i have if it is compatible and it is. I was also using this pc prior with the old psu, no gpu (only integrated), and old hdd.

pss: please do use simple terms too because I’m a newbie to this 😔