[SOLVED] HELP: Everything inside the case is on, but not outside!

[thuannt05]

So I read this post but it doesn't seem to cover my problem: https://forums.tomshardware.com/thr...deo-output-troubleshooting-checklist.1285536/

My new system is built 2 days ago, it was fine until today. It suddenly turned off twice, and when back on, everything inside the case is on, fan spinning AS IF nothing was wrong, but mouse/keyboard wont light up, monitor won't have signal, not even BIOS post screen.
I've tried:

• Reseating RAM sticks/slots.
• Reseating CPU
• Reset by removing mobo battery.
• Use graphic card output and still nothing on screen (also mouse/keyboard won't response, but everything in case light up/spinning)
• Remove onboard graphic card, still nothing on screen (also mouse/keyboard won't response, but everything in case light up/spinning)

I managed to turn it back on once. But it will just turn itself off again after 10 minutes. And it will just have the same symptom: everything inside the case seems normal but nothing reponse, no BIOS post screen.
After that I tried switch to another PSU, it would just remaining like that. I'm pretty sure the PSU is not the problem because I'm on the computer which I switch the PSU with the new system.
My main suspect is the motherboard? Anyone with a hint? Thanks
System as follow:
i5 11400
Gigabyte B560M Aorus Pro AX
RAM G.skill F4-3600C18D-16GTZN
Graphics: tried both onboard and GTX970 outputs

Thanks in advance
Update:
It also has this symptom: "It may power on for a second or two, but with no cpu in place it will shut itself down." - I quoted it since I read it in another thread.

 

[popatim]

Power supply?

 

[thuannt05]

Power supply?

Tried switch 2 PSUs and I'm 100% sure the PSU are fine, tried both on other computers.
update: it also has this symptom, could also be CPU? "
"It may power on for a second or two, but with no cpu in place it will shut itself down." - quoted cuz I read this in another thread and my system also has this symptom beside those I wrote above

 

[popatim]

You need to have a CPU & Cooler installed.
The motherboard cannot boot up without the CPU but while you have it off make sure you have no bent pins. Be sure to clean off the thermal paste and reapply new paste when you install it.