[SOLVED] Asus H110Plus motherboard (New Build) fails at power on

Aug 27, 2020
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New build with no other hardware installed except:
Asus H110Plus motherboard
i3 9100r CPU
Generic DDR4 4GB RAM
Generic PSU 600W

With the ATX 4 pin connected, when powering on, fans turn on, mobo lights up, then all turns off after 1 second. Removing the ATX input will result in either running for 5 seconds then turning off, or running indefinitely. There's no PC speaker so I can't hear any errors. I measure 12.4V on the ATX and resistance of the mobo connector is >1K ohm.

Is there something else I can test to confirm motherboard or PSU?