Why Does My PC Randomly Shut Off?

Short answer: Sudden shutdowns almost always come down to power or cooling. If the CPU is overheating, the system cuts power to protect itself. If the power supply cannot meet demand, or cannot pull steady power from the wall, the same thing happens. Check temperatures first because it is the quicker test, then work through your mains power, then stress test the hardware to find the failing component.

A PC that powers off without warning is telling you something specific, and it is usually one of a small number of things. Here is how to narrow it down without guessing.

First, is it a shutdown or a crash?

These get used interchangeably and they point in different directions.

• A sudden shutdown powers the PC completely off. You have to press the power button to bring it back.
• A crash generally results in the PC restarting itself after powering off. This behaviour can be changed in your UEFI/BIOS.

This guide is about the first one. If your PC restarts itself, or you get a blue screen, you are looking at a software or driver problem more often than a power one.

The two usual causes

Cooling. When a component gets too hot, usually the CPU, it triggers Over Temperature Protection and the system cuts power rather than damaging itself. This is a safety feature working correctly, and it is a symptom rather than a fault in itself.

Power. Components cannot pull the power they need. Either the power supply is not able to meet the system's demands, through being underspecified or through degradation over time, or it is not able to pull steady power from the wall.

Step 1: Rule out overheating

This is the faster of the two to test, so start here. Watch your CPU temperature during startup and for the first few minutes after logging in to Windows, and then during whatever workload triggers the shutdown.

If temperatures climb rapidly towards the high 90s and the shutdown follows, you have your answer, and the investigation moves to why the cooler is not doing its job. Common causes there include a cooler that has worked loose, fans that are not spinning, a radiator mounted so that air has collected in the pump, or a badly clogged dust filter.

If temperatures look normal right up to the moment it cuts out, cooling is not your problem. Move on to power.

Step 2: Test the power coming from the wall

This is the part people skip, and it catches a surprising number of cases. The PC may be fine and the electricity reaching it may not be.

• If you are using a UPS, surge protector or plug strip, temporarily connect the PC directly to the wall to see whether the behaviour changes. Temporarily is the operative word, see the note below.
• Try an outlet on a different circuit in your home or building.
• Try a different power cable. NZXT prebuilt PCs use a standard NEMA 5-15 to C13 cable, and the gauge should suit your PSU rating.

Do not leave your PC on direct wall power. Running direct to the wall is fine as a diagnostic step, but it leaves the machine unprotected against power surges. For everyday use, always have your PC on a surge protector or a UPS.

Brownouts are the hidden culprit

Worth understanding the difference, because one of these is much harder to spot:

• A blackout is a sudden full loss of power, usually a problem with the grid. Your whole home goes dark, so it is obvious.
• A brownout is a momentary drop in power, usually caused by something on the same circuit drawing more than the circuit can supply. Your lights dimming when the washing machine kicks in is a brownout.

PC hardware is very sensitive to brownouts. A drop far too brief for you to notice is enough to shut a PC down. If your shutdowns correlate with an air conditioner, a tumble dryer or a vacuum starting up somewhere in the house, that is your answer, and a UPS solves it.

Surge protector or UPS?

A surge protector is a plug strip with a fuse or switch that trips when it detects a surge. It is the first line of defence for your PC. Note that not every plug strip is a surge protector, so check the packaging and look for a surge protection rating of at least 2000J.

A UPS, or uninterruptible power supply, is a battery backup. It typically includes surge protection and power conditioning, and it keeps the machine running through a sudden loss of power. When choosing one, get a rating that exceeds your PC's power supply.

Our general recommendation is a surge protector rated 2000J or higher as the minimum for setting up a PC safely. Step up to a UPS if you want additional protection, or if you experience brownouts.

Step 3: Stress test to find the failing component

If cooling is fine and external power is fine, the next step is to find out which component is failing under load. A stability and stress testing program such as OCCT generates artificial workloads that expose hardware faults far faster than normal use will.

Run each test for its full duration, or until it triggers the fault. Note which test causes it.

CPU test

• Mode: Extreme
• Load type: Variable
• Thread settings: Auto

The CPU+RAM and Linpack tests apply additional load if you want to push further.

Graphics test

Use the Combined test with 3D Adaptive and VRAM active.

• 3D Adaptive configuration: Steady
• Priority: Realtime
• Load type: Extreme
• Memory: 80% or higher

These can be run individually, but combined does a better job of exposing graphics card faults.

Power supply test

The Power test loads every component at once, which is exactly the condition that forces a marginal PSU to give up. No configuration needed.

OCCT also includes memory and storage tests, though issues with those components rarely cause sudden shutdowns.

OCCT is free for personal use and cannot be used in a commercial or business environment. Support options are offered when starting a test and on the OCCT website.

Step 4: Act on the result

If a test caused a shutdown, run that same test again to confirm the behaviour is consistent. One-off events are not diagnostic. A repeatable failure on a specific test points at a specific component.

From there:

• Within warranty: contact NZXT Support. All NZXT prebuilt PCs carry a standard two-year limited warranty.
• Out of warranty: the component the test targeted is the one to replace. NZXT does not offer out-of-warranty repair, but our prebuilt PCs are built using standard off-the-shelf components, so they are straightforward to repair and upgrade yourself or through a local shop.

Frequently asked questions

Why does my PC shut off only when gaming?

Gaming loads the CPU, GPU and power supply hardest, so it surfaces both overheating and power delivery limits. Check temperatures during a session first, then run the OCCT Power test.

Can a failing PSU cause random shutdowns?

Yes. A power supply that is underspecified for the system, or that has degraded with age, will shut the system down when demand spikes. The Power test is designed to reproduce this.

My PC shuts down when my air conditioner turns on. Is that related?

Almost certainly. That is a textbook brownout. A UPS with power conditioning will resolve it.

Does a surge protector help with brownouts?

Not directly. A surge protector defends against voltage spikes, not drops. Some include power conditioning that helps smooth delivery. For brownouts specifically, a UPS is the right tool.

How hot is too hot for a CPU?

Modern processors are designed to run at 80 to 90 degrees Celsius during intensive work, so high temperatures under load are not automatically a problem. Sustained temperatures at the very top of that range, or a shutdown coinciding with a temperature spike, are.

Could this be a Windows problem rather than hardware?

A complete power-off with no restart and no blue screen points to hardware or power. If the system restarts itself or blue screens, that is far more likely to be a driver or software issue.

My PC shut down and now it will not start at all. What do I do?

That is a different problem and it has its own order of operations. Confirm mains power, disconnect peripherals, then reseat the RAM and graphics card. Our guide to a PC that will not turn on covers the full sequence.

Need help narrowing it down?

If you have run the tests and want a second opinion on the results, send them to us. Our team is at NZXT Support.