GA-H270N-WIFI Motherboard - PSU keeps shutting down

[hamspam]

Hi,
I just built a new system with this (GA-H270N-WIFI) as the motherboard. It's run for >48 hours with no temperature issues, an install of windows and a download of gigabytes of stuff. Now it won't power up, the PSU keeps shutting down and restarting continually. Interestingly I had this happen once while building/testing the system. But I assumed (at that point) it was just something like a poorly seated GPU (EVGA 1050Ti) card.

Here's what I've done to debug:

• Dismantled the build - have just the motherboard and the PSU on an anti-static workmat.
  No RAM, GPU, case cables, no fans connected etc.
  The processor (Intel - Core i5-7500) is still in the socket, but I'm not connecting the 12V PSU to it.
  I connect just the main 24pin ATX PSU cable and power the board by touching a jumper across the power button pins.

The PSU fan comes on and the MB boots up. Seconds later, audibly the PSU clicks off and the fan stops (we never get to the BIOS) and we stay in this power up loop

So I think we are looking at the PSU or motherboard. I tested the PSU (Corsair CS650M) with another old motherboard and it runs just fine. Motherboard BIOS settings unchanged, it's all stock.

Any ideas for things I can test/try before I send the MB back?
Now of course I'm in a dilemma about whether this is a compatibility issue or a faulty MB.

I had no issues during the build, I was very careful and I don't see how I could have damaged anything.

Thanks in advance for any comments
HamSpam

[shadowsports]

The MB requires 24pin, ATX_12v and CPU_FAN connected in order to run.  It won't POST without these connections. Since you haven't posted your system specs, please share your memory brand and model.  Is it on the QVL for your board?

You said the board ran successfully for 2 days?  And now won't post.  Did you update the BIOS by any chance?  Are you trying to overclock? 

Common causes for Boot loops are:
Incompatible memory
Unsupported CPU / BIOS rev
Bent PINs in CPU socket
Aggressive BIOS settings
Incorrect power connections
Defective MB or system component

We don't have enough information about your system to make anything more than a guess at this point.  Since the PSU appears to work elsewhere, it could be the board, but' I'd try the following:

Disconnect power to board, leave battery connected and use flat blade screw driver on CLR_CMOS jumper next to SATA ports.

Perform a battery pull (3-4 min), then retest.  I think it has a header plug on this board   

If unsuccessful, try invoking start from the back up BIOS.  By the sounds of it you may not get that far.  Try with only 1 stick of ram installed in DDR4_1 (closest to CPU socket).  If you can test with another PSU, great.  That should probably give final confirmation if nothing else works.