The BIOS of some mainboard manufacturers compares the speed of the fan with a specified value. If the fan speed does not match the specified value, either the PC emits a warning or switches off. Contrary to the temperature control, the RPM control is of no importance, since fan speeds will be between 500 and 7000 RPM depending on the type of fan. This RPM control can be deactivated in the BIOS settings. Please consult your mainboard manufacturer for more information regarding these settings. Instead activate the temperature warning. This protects your CPU also from other cooling problems than a failing fan.
In the case of the PC is not booting or immediately switching off, attach the plug of the cooler to the auxiliary power of the mainboard and attach a second fan with higher RPM to the primary power socket. Now the PC can boot allowing the RPM control to be deactivated in the BIOS settings. We recommend using a temperature control instead of a RPM control. The cooler does not need to be removed from the processor for this procedure.