Have a look here and check you have power supply cables where they're meant to be.
"No POST", "system won't boot", and "no video output" troubleshooting checklist This checklist is a compilation of troubleshooting ideas from many forum members. It's very important to actually perform every step in the checklist if you want to effectively troubleshoot your problem. 1.Did you...
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Can you give more information plz, on specs and what components were tried.
X470 would need a bios update to run 3rd gen using a 1st/2nd gen Ryzen to do the update.