Just replaced mobo, now turns off immediately. Now what?

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mb91

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Last week, I was happily coding away on my best machine that's about 7 years old when it just shut itself off and stayed utterly dead. So I ordered the same model mobo for a replacement, and I just finished putting it all together, and now it will only stay on for a second before shutting off again. But at least this time it doesn't stay dead; it'll keep on turning on then off every time.

Computer: Self-built desktop
Mobo: ASUS Z97-A / USB 3.1
CPU: Intel Core i7-4790K CPU @ 4.00GHz
RAM: 2 x G.Skill 8GB DIMM DDR3 PC3-21300U
PSU: Corsair RM 850W

Now at first I figured the PSU died or had some problem(s), so since I own an Antec digital PSU tester, I hooked it up and let it run for several hours. There was not even a tiny blip of a problem -- the PSU is perfect.

The only other reasonable possibility was that the mobo died, which is why I ordered a replacement. And that new board is picture-perfect, not a bent pin or other defect can be seen.

I'm pretty good at this system building and troubleshooting, having assembled about 16 of them, but I'm stumped this time. I would just go all trial and error, but given what's happened, I'd be a total moron if I didn't ask for your advice and suggestions.

What should I do next, please?
 
Do not put faith in PSU testers like that. PSU testers put practically no load on the PSU. They are only good to see if the PSU will turn on and what voltages it can supply at no load.
I'm betting the PSU can't supply enough power to sustain the system, so it shuts down to protect the motherboard and peripherals from damage.
Replace your PSU. Borrow one from a friend to test if you can. Use the cables that come with the new PSU (do not re-use old cables since modular cable pinouts are often times incompatible between models/brands).
 
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Yep, you make a lot of sense. Thank you! Just ordered a replacement,,,
 
I just had a similar situation...did the replacement PS fix your issue?

In my issue I've tried 2 sticks of ram, 3 power supplies, pulled motherboard out of the case...

I ended up doing a new build and re-using same powersupply without issue, so I figure it's the motherboard or processor.
 
well, maybe if you turn it on/off fast enough you can still use it for gaming :barefoot:
 
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