New build crashing

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I built my first PC last week, with help from you all here. It worked fine for a week, but today it started shutting down randomly, and I could use some help diagnosing.
The build is a Ryzen 5 3600, with GeForce GTX 1660 Super, a 1tb M.2 Inland SSD, 16gb of Vengeance RGB Pro DDR4-3600, Asus B450F ROG Strix, and CX650M 650 Watt 80 Plus Bronze PSU.
It started when my daughter was playing Roblox, just a sudden and full shutdown, no warning or glitching. I replicated it playing Skyrim on Steam, then just poking around on the PC. I booted to Bios, reset the RAM to "auto" (I had set it to 3600, that's the only tweaking I had done). Then I tried Windows diagnostic and HCIMemTest and it shutdown during both. I loaded bios and was about to boot to MemTest86, and it shutdown before I could even edit the bios.
Both cpu temps and voltages seem to be within a normal range. I'm not sure what else I should check at this point. Buy some new RAM and test? 
Any advice? Thanks in advance!!

Comments

  • PowerSpec_MikeW
    PowerSpec_MikeW PowerSpec Engineer
    5 Insightfuls First Anniversary First Comment 5 Awesomes
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    Please clarify what it's doing? Is it shutting down and staying off then you have to turn it on? Power or heat.

    Is it rebooting itself? Intermittent power loss most likely in this case.

    Sounds like it's the former. And doing that with the windows memory diagnostics which run outside the OS really narrows it down. Check your temps, they're unlikely the issue. At that point you've got to look at the power supply or the motherboard. Swap the power supply first.


  • jessefive
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    Thanks. I just got done breadboarding it, just CPU, gpu, motherboard, and 1 stick of RAM, and it did the same thing, even sooner. Instant shutdown, no warning and no restart. Now it won't even get to bios. Seems like it's either PSU or board, right? I don't have a spare of either to test, so it looks like I need to go back to the store
  • PowerSpec_MikeW
    PowerSpec_MikeW PowerSpec Engineer
    5 Insightfuls First Anniversary First Comment 5 Awesomes
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    Yes, probably the board at that point. You can check the PSU by shorting it on with a paper clip or a jumper if your PSU included one. If it'll power on, seems unlikely you wouldn't get a brief moment of power, to indicate a short or a rapid shutdown. I would do that if you're comfortable, if it powers on, board seems more likely to me. If you're not, stay with the plan of starting with the power supply, just because it's easier and faster to swap.

    As more background, a system shutting itself down without a power failure, is the system attempting to protect itself. It's either seeing a temp that's in the shutdown range, or it's seeing a voltage that's outside the limits of the specifications on a certain rail. This is usually about +/- 10%.
  • jessefive
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    When it shuts down, I can see that the mobo is still getting power via an rgb light. However neither the case switch or the 2pin bridge will restart it until I turn the PSU off then on again. So I suspect the PSU is at least working. I'm not sure if that really narrows it down though.  I tried to monitor both temps and voltage when it was on, and neither seemed that far off.

    I might just return and replace both. The local store isn't very close to me, so I'm trying to minimize trips
  • PowerSpec_MikeW
    PowerSpec_MikeW PowerSpec Engineer
    5 Insightfuls First Anniversary First Comment 5 Awesomes
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    That's understandable, and no it doesn't. You have standby power. Reseating the 24 pin or discharging the PSU will work to power it back on. That's just in an indication that the device powered it off and it's going to retain that until it's discharged. The board in this case. It's one or the other, swapping both makes sense if it's a long drive.
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