Question 2013 self-build, frequent shutdowns

Oct 6, 2019
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First, desperate post, please be gentle and forgive any bad forum etiquette on my part!

I have a 2013 self-built PC that, after five years without issue, has been experiencing frequent, random shutdowns for some time. It can happen while I'm working or when the computer is doing "nothing", and it can also happen five minutes after startup. It shuts down completely for a second or two, then tries to restart. On every occasion, it's only the case fans (x2) and CPU fans that start up. The display doesn't power on again, no drives or peripherals come back, and I have to press the power button to do a hard shutdown. If I then try to restart within a minute or two, the same fans-only situation reoccurs. However, if I leave it for, say, fifteen minutes, everything restarts and reboots as it should.

Infrequent video editing aside, I don't use the machine for gaming or anything particularly taxing. Office applications, browsing, watching videos. It sits off the floor, it's cleaned regularly and there's lots of space inside the case.

To keep this post as brief as possible, I won't give an exhaustive list of all the things I've tried in an attempt to isolate the problem hardware. I have disconnected everything except the OS SSD, tested again with a different OS SSD as the only other thing connected to the motherboard, always the same shutdown problem.

Not having a spare PSU or motherboard to hand makes it more complicated obviously, and I really don't want to spend money on new ones before knowing which part, or both, if any, is failing.

Very grateful for any advice on a how I might proceed, please let me know if I need to give more information.

Intel i5-4670
MSI H87M-G43 ATX Mboard
Seasonic G-360 PSU
1x SSD, 1x 2TB HDD, 8GB DDR3 RAM, Arctic Cooling Freezer i30
Fractal Design Define R4 case
 
Oct 6, 2019
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As far as I can with any confidence, Kamal. :unsure:

I've tried using Speedfan and hwinfo to watch and log temperatures, neither shows any core getting much above 30°C. I've rebooted into the BIOS too with its own on-screen temperature monitor never going above 40°C. I've never left it to run there long enough to see if the system shuts down from the BIOS screen too.

Does it appear like an obvious temperature issue from the symptoms I described?