Why won't my PS4 Pro stay on

I recommend having a look at this guide here on IFixIt!

PlayStation 4 Turns On Then Back Off Repair

That could be the issue, it’s also a symptom of a bad apu. What happens is the solder balls on the APU Will overheat and sometimes crack causing a Loss in APU functionality Which leads to the device being turned off immediately during the self check portion of the initial start up. If you’ve already replace the power supply and you’re still having the issue then it’s probably the APU you can try installing some washers around the area of the APU which will clamp down the chip and Hopefully restore The current flow through the chip and fix your issue but if not you’ll most likely have to have your APU reflowed. Look online for ps4 apu quick fix with washers and you can try it out.

Hello guys!

As late as I am(about 3 years since the first post :)) ), I found a solution to this same problem.So after cleaning my ps4 pro ,I placed back the power supply ,but didn’t pay attention to the 2 silvery connectors that should fit inside the power supply, each with its own place, and bent one of them down touching the other one.This way the power wasn’t flowing as ps unit was seeing a shortcircuit.So I got both straighten up ,fitted each in its own hole and my PS4 PRO is back in action.Hope this helped !Good luck and Have fun!