Question New pc not turning on

[Faxlim]

ROG STRIX Z390-F GAMING motherboard CPU light flash red for a second (the fans turn on for a second as well) and then the computer shuts off. I have isolated it to the small ATX power connector, any help?

EDIT: The 8 pin ATX power connector seems to work with different motherboard..

 

[rgd1101]

full system spec? include make and model of the psu