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Why does my PC shut off randomly shortly after startup?

August 22, 2026 3 answers
Asked by MellowCedar47
I recently got this PC from a friend and reset it, but it now powers off without warning, usually within the first few minutes after starting. It can happen while the computer is idle, opening browser tabs, or browsing files—not just during demanding tasks. I'm trying to troubleshoot it myself because I can't afford a repair-shop diagnostic fee. Could the power supply or an old power cable be failing? There's no visible damage to the cable, but I had to use one supplied by my dad. The known hardware is an Intel i7-9700 and an RTX 2080 Super.
failing PSU Hardware loose power cables old power cord PC overheating random PC shutdown RTX 2080 Super

Answers

OrbitLime82
Start by checking temperatures with a hardware monitor. If the CPU is hitting around 100°C, or the GPU is overheating, the system may shut itself off for protection. Clean out dust, confirm that all fans spin, and inspect the CPU cooler. Repasting may be necessary if the cooler is poorly mounted or the thermal paste has dried out.

MellowCedar47: It turns back on immediately, and the fans seem to run normally. I’ll check the temperatures while it’s running.

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CopperFalcon58
A sudden complete shutdown usually points more toward overheating, a bad connection, or a failing power supply than ordinary Windows corruption. A reset won’t fix a weak PSU. Check the PSU’s brand, model, and wattage, and test with a known-good, properly rated replacement if possible. Avoid repeatedly stressing the system until you know the temperatures and power supply are safe. After the hardware checks, update the BIOS, chipset, and graphics drivers and run a memory test if the problem continues.
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QuietMarble6
Since the PC was moved and you don’t know its history, unplug it and reseat the main connections: the 24-pin motherboard cable, CPU power cable, GPU power cables, RAM, and graphics card. If the power supply is modular, check both ends of every cable. Also make sure the wall cable is fully seated, though the cable itself is less likely than a failing PSU to cause a complete power cut.

VividNectar31: The inside is pretty messy, so a loose connection is definitely possible. I’ll check the cables and RAM before doing anything more complicated.

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