Question Computer randomly shutting off, already replaced PSU

Jan 7, 2020
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i helped my roommate replace some parts on his PC and everything was working well until the other day he said it kept randomly shutting off while he was using it, then it finally just wouldn't turn on (no lights, no boot, nothing). so considering we replaced the RAM, CPU, and MOBO when we upgraded, my initial thought was it was the nearly 10 year old 500W PSU that had finally go bad. He replaced this with a 750W PSU and initially upon trying to boot, it would start up with ONLY the CPU fan spinning, but no case fans. it did not appear to boot into the BIOS, then would die and start back up in a loop. after flipping the switch on the PSU on and off a couple times and getting the same result, it finally booted up normally so we called it a day. after about a day of it working fine it started to randomly shut down again during use. virtually all parts are brand new and less than 2 months old besides the case itself. we tried cleaning all fan connections to the MOBO in case any dust was causing issues with fan feedback, and still the same issue persists. I'm wondering if maybe the old PSU went bad and fried the MOBO and possibly the CPU with it (he would leave his computer on for weeks on end).
dont have full specs as i'm not near the build currently and my roommate is virtually clueless about all of this.
SPECS:
CPU: i7-8700k
MOBO: some ASRock Board
RAM: DDR4 2133 (single 8GB Stick)
PSU: 750W
GPU: GTX 1060 4GB

any help would be appreciated!
 
Jan 6, 2020
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I had a vaguely related issue while setting up my current build. It worked fine until I installed the fans, then all of a sudden, powering it up got all the fans spinning for about one second, then everything would go dead. I swapped out my PSU and tried several other things, tearing my hair out in the process, until I unplugged (of all things) the RGB interface from the header (RAINBOW1 on my MSI board), and BAM! Everything worked perfectly. No idea why. I instead hooked it up to the second RGB header on the board (RAINBOW2) and it worked fine. Super weird, but the point of the story is that literally any cable plugged into any header could cause a short, so I would try systematically unplugging everything and powering on, one at a time.
 
Jan 7, 2020
2
0
10
0
I had a vaguely related issue while setting up my current build. It worked fine until I installed the fans, then all of a sudden, powering it up got all the fans spinning for about one second, then everything would go dead. I swapped out my PSU and tried several other things, tearing my hair out in the process, until I unplugged (of all things) the RGB interface from the header (RAINBOW1 on my MSI board), and BAM! Everything worked perfectly. No idea why. I instead hooked it up to the second RGB header on the board (RAINBOW2) and it worked fine. Super weird, but the point of the story is that literally any cable plugged into any header could cause a short, so I would try systematically unplugging everything and powering on, one at a time.
i'll definitely give that a try. he installed the PSU himself and i didn't give it much more than a quick scan afterwards so its very possible a plug could be in the wrong slot.
 

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