fan overheat warning on boot up

[Cody77]

I updated windows 11 and when the computer restarted it did not boot up as normal. The screen was black with basic white text. To summarize it said there was an error with the computer's fan and it would power down after 15 seconds. I hit the boot on anyway option to not interfere with the update install. The desktop has three small fans at the front that seem to be working fine, but I see a larger fan at the back that is moving very slowly. It's moving about as fast as the second hand on a clock. It stop and starts like the ticking of a clock as well. 

[WAWood]

Case fans (fans mounted in the computer case) are nearly always connected to fan headers on the motherboard that allow Windows to control the speed of the fan.  When the PC is idle, the fans slow down, often to the point that they are not heard,  When the PC starts getting used, the fans speed up.

What I have done to test a fan is shut down the PC, disconnect the fan power lead from the fan header on the motherboard, and using an adapter, connect the fan power lead to a power lead from the Power Supply Unit (PSU).  That runs the fan at a steady speed, and since these fans often have sliding switches that allow different speed settings, I slide the switch through all the position to test all the speed settings.

You will need to do something pretty much the same -- and if you are not comfortable doing this yourself, we have no way to walk you through that, as we have no access to your PC, so you will have to take it to a PC repair shop and pay them to do it for you.