My PC randomly powers off, and it won't reliably start working again until it has been left alone to cool down or rest for a long time. Removing the case panel temporarily helped, but the computer shut down again after about 30 minutes of gaming once the panel was replaced. I checked the thermal paste and monitored temperatures with HWMonitor, but nothing appeared unusually hot. It also shuts down while sitting in the BIOS, and the longer it remains powered off, the longer it seems to run before shutting down again. Removing the GPU made no difference, and connecting the PC to a UPS did not help or trigger any power warning. What hardware or diagnostic checks should I try next?
4 Answers
The power supply is the first thing I’d investigate. A failing PSU can shut the whole system off without producing a blue screen, especially once it warms up. If possible, test with a known-good replacement PSU that has enough wattage and the correct connectors.
It could still be a storage firmware or background-software problem in some cases, but shutting down while in BIOS makes that much less likely. I’d start with a different PSU, then test with only the essential hardware connected and inspect the motherboard for damaged components or loose power cables.
Even if the temperature readings look normal, check that the CPU cooler is firmly mounted. A broken bracket, loose pump, or poor contact can make the cooler appear installed while the processor actually overheats. Check the cooler mount, fan or pump operation, and CPU temperatures immediately before shutdown.
Because it also happens in the BIOS, software is unlikely to be the main cause. You can check the system event logs for unexpected-shutdown entries, but those usually only confirm that power was lost rather than identify the faulty part. The PSU, motherboard power circuitry, and cooling mount are the most useful areas to test.

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