fix pc

Hello, all. I'm new to the forum. I am trying to diagnose why my old PC no longer turns on. I'll preface this all with the fact that I'm not an experienced builder, and this is the only PC I've ever built, which was 9 years ago. I've tried reseating all connections, reseating all components...

my MSI z370 Pro Died after i connected a used bought SilverStone PSU (750 Watt) Silver rating (I know i made a biggest problem buying a used psu) the Guy wont agree to return the psu nor agree that his psu is faulty ... so short story he was a scammer as soon as i connected the psu my sades k14...