What to Do When Your PC’s Fans Spin Up at Full Blast the Moment You Turn It On

This article was automatically translated from Japanese using AI. The Japanese version is the authoritative version.

When you turn on your computer and the fan starts spinning at full blast, you might worry that the machine has broken.
When a computer suddenly starts behaving strangely, it’s easy to assume there’s nothing you can do, but you can often fix these problems yourself.

That said, you do this at your own risk, so be very careful, and if you know someone knowledgeable, it’s a good idea to work on it together.
Computers are expensive, after all…

In this post, I’ll describe—based on my own experience—what to do when the fan spins at full speed at startup and doesn’t calm down even a while after Windows has booted.

Symptoms

I had left my desktop computer on overnight, and in the morning I noticed the fan was running at full speed.

I shut the computer down once, but the fan kept spinning, so I flipped the power supply switch off and unplugged the power cord.
I pressed the power button a few times to discharge it and then booted up, but the fan was still running at full speed.

Other than booting somewhat slowly, though, there were no other apparent problems.

What I did

I checked the CPU temperature in the BIOS setup screen, but it only reached about 30 °C, so there was no problem there.

I set the PC to power-saving mode in the BIOS, but nothing changed.
I also lowered the minimum fan speed, with no effect.

I unplugged every cable connected to the computer, including the power and USB cables, pressed the power button a few times to discharge it, and then opened up the case.

I removed the coin cell battery and pressed the power button several times (clearing the CMOS).
[There are other ways to clear the CMOS. It’s also a good idea to disconnect the power supply cables to the motherboard at this point.]

Clearing the CMOS is a way of resetting the motherboard’s BIOS: after removing the coin cell battery, you drain the residual electricity from the motherboard.

I put the coin cell battery back in, reconnected the keyboard, power, and video cables, and turned the computer on.
The fan then returned to its normal speed.
Just to be safe, I also updated the BIOS.

For now, everything is running normally.

Cause

The direct cause seems to have been a BIOS error.
Something apparently went wrong, resulting in the fan running at full speed.

BIOS errors can often be fixed by clearing the CMOS, so whenever you suspect a BIOS error is to blame, resetting the BIOS with a CMOS clear will frequently solve the problem.

BIOS errors can be caused by leaving the computer powered on for long periods, dust building up inside the case, shutting the computer down abruptly at an inopportune moment, or installing dubious software.

Dust buildup inside the case is especially common, so you can prevent it by cleaning the interior with compressed air about once a year.

I updated the BIOS at the end this time. The reset alone is probably enough, but updating may also clear latent errors.
It’s the same idea as a camera that won’t power on starting up again after a firmware update.

Being able to fix computer errors yourself is a genuinely valuable skill, since it saves on repair costs.
Also, when a computer won’t boot, there are surprisingly few things you can do besides replacing parts, so it’s worth looking into other options first.

Bonus

I’ve decided to offer consultations on computer problems through Coconala!

I’ve worked with all kinds of computers and seen all kinds of problems.
My Coconala listing mentions computers that won’t turn on, but I’m happy to help with any trouble you run into while using a computer.

I’ve only just started using Coconala, so I may still be getting the hang of it, but please give it a try the next time you run into computer trouble.

I use both Mac and Windows, so I can help with problems on either platform.