Turned on my laptop and suddenly my fans start spinning like crazy.

Hello, welcome to our community.

The high speed of the fans could be because of the high temperature of your laptop, download some monitoring program and monitor CPU, memory and disk usage to see if this is the problem.

This topic can give you more details on why this is happening. (Click here)

(This is not a Microsoft website but it contains reliable information.)

The BIOS can do that. Its what controls the system fan speed. I've had my own system BIOS do that erroneously on reboots when it shouldn't have. The current one (got one last one whew) so far does not have that issue same as all the others before the bad one as well.

So you could look into if there's a BIOS update available. That can of course come with other problems or it might not or might solve another problem. No way to know ahead of time.

But, if your computer was cooled down (off for a while as you suggest) then it shouldn't be heat as Patrick suggests unless you had it sitting in heat.

Hello, I'm Jan and I'm happy to help you today. I'm sorry that you are experiencing this problem. If the fan is spinning at maximum speed at startup might indicate that it is trying to cool down the CPU/GPU/internal components. Here are some things you can try.

1. Disable unnecessary applications programs that are running from the startup to reduce the CPU load

Try these steps
Press CTRL+ALT+Delete
Then click on Task Manager
Then Navigate to Startup Tab
( from there you can Disable unnecessary applications running from the startup)

Perform a Clean Boot to disable unnecessary startup and services
https://support.microsoft.com//topic/how-to-per...

2. Boot your computer in BIOS and check for fan speed control settings. Also, Laptop Manufacturers have software that has fan speed controls, temperature power monitoring. From there you can check the laptop temperature.