I just bought a ROG CROSSHAIR X670E HERO, connect all cables and power supply, the start button and the flex key button flash quickly.
The system does not boot.
I unplugged video card changed ram but no change.
A thousand thanks
Ensure all power connectors are fully inserted.
If using extensions, remove and try using OEM PSU cables.
Ensure motherboard stand-offs are correctly installed in the chassis.