Causes and Possible Fixes When a CPU Fan Turns off at Windows Start

Causes and Possible Fixes When a CPU Fan Turns off at Windows Start
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Why Won’t My PC Fully Boot?

It’s always good to hear the familiar Windows chime when you boot up your PC. From the speaker “beep!” that occurs when you first power up to the quiet rattle of your hard disk drive, booting up is like starting a car and the Windows chime (or whatever custom sound you might have applied) is the equivalent of your first press of the accelerator.

And just like when your car fails to start or even turn over first thing in the morning, the Windows chime can herald not the beginning of a fun browse around the web, but a nightmare as your PC shuts down.

One common hardware reason for this occurring (amongst a myriad of software reasons) is that the CPU fan turns off as Windows starts, and the motherboard shuts down as a precaution against damaging your CPU from overheating. This is particularly common in laptops, but shouldn’t happen on a desktop computer.

But why does this happen?

Why Does the CPU Fan Turn Off at Windows Start Chime?

The cause of this problem can be difficult to trace, and might be due to several factors:

  • Broken fan
  • Power distribution issues caused by power supply unit (PSU)
  • Damaged motherboard
  • Old or unsuitable mains power cable

Open your PC tower to find out why the CPU fan turns off at Windows start

It is also possible that malicious software is causing this to occur, particularly if the process can be repeated and occurs around the same point on each occasion.

We can test if is a hardware problem by opening the case and stripping down the number of items connected to the PC/motherboard to the basics:

  • keyboard and mouse
  • video output to monitor
  • 20+4 power cable from PSU to motherboard
  • 4/8 pin 12v wire both coming from the PSU to motherboard,
  • CPU fan connector
  • power and reset button to the case
  • case speaker

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Why Should I Do This?

What we’ve done here is disconnect hard disk drives, any solid state drive you might have, and backup drives and optical drives and any card readers or USB devices. (If you have any concerns about opening your case and removing cables, you should either speak to a specialist or grab a friend or colleague to assist you.)

The next step is to switch on your computer – leave it running for a while. You should see notification on the monitor that no disk can be found, and the computer might force itself into a reboot every so often, but in most cases the fan will still work. If the fan stops, however, your first step should be to replace it.

Tracing the Fault

As your CPU fan turns off at the Windows start chime we can probably rule out the motherboard and processor as faults here would prevent Windows from even booting.

The next step is to try a different power supply unit, working under the assumption that as Windows boots and different programs are accessed, they might be kept on different hard disk drives which are then both accessed together. This simultaneous draining of power might be the thing that prevents power getting to the fan and shutting down the computer.

After you have tried a different PSU without success, connecting components to the motherboard and PC chassis one at a time and switching it on to test each should help you determine the troublesome part.