Question Asus Prime Z270-A takes multiple attempts to boot after power has been disconnected

[egg0]

My PC attempts to boot once then turns off then boots again to Bios before it will boot from the harddrive.

Video of the sequence here: https://streamable.com/rk4h4m

PC information:

There does not seem to be any cause it just started happening one day.
The fact that it only occurs after power is disconnected makes me suspect a battery failure on the mother board?

Any insight would be appreciated.

 

[rgd1101]

brand and model of the psu?

 

[egg0]

Just checked now.

PSU is EVGA 650 G2 Gold power supply approximately 5 years old.