Need help diagnosing my pc

Hello and sorry this is a bit long, i am requesting the help of the great people of this subreddit to help figure out what the issue with my pc is, so lets get into the issue, my pc simply won't turn on, its not a fresh build, at the end of 2022 i decided to upgrade my pc, brought new mb, ram, gpu (off marketplace) and cpu, i installed it all and it worked fine, a couple months later, pc shuts off at random, i simple ingored it and turned it back on, worked fine for about another month, shuts off again, ingored the issue for the next like 3 weeks until it no longer turned on, which i know was stupid of me to ingore the issue but i didn't have the funds to possibly repair it then late-mid 2023 my friend brought me a new PSU, installed, still ran into the same issue, i have had the MB send off and tested and it was fine, when i put it back together it worked until it ran into the same issue, have tested the ram in the computer by switching them out and putting to different slots to test it and nothing, it has been a year since i have played any games or been able to hang out with friends and i miss it, so i would really like some help thanks

TLDR, pc won't turn back on after randomly shutting off a few times after upgrading, new mb, ram, gpu (off marketplace), cpu, psu (replaced it once issue happened), had motherboard sent off and tested (was fine), slot tested the ram and nothing changed