When a computer overheats, it can suffer severe performance degradation. To prevent overheating, computers typically use fans to dissipate heat and cool the system. If cooling was the only concern, fans would always run full blast, but this increases power consumption and noise. Therefore methods of controlling fan speed are offered to allow users greater control over system fans according to their priorities. One way to control fan speeds resides in the "basic input output system," or BIOS. Unfortunately, not all manufacturers offer this option in BIOS.
Reboot your system into BIOS. This entails pressing a key, or combination of keys, during the boot process. Your computer or motherboard manual should tell you exactly what key(s) to press, but usually it will be either F1, F2, DEL, ESC or F10.
Look at the top or left side of the BIOS screen for the menu options. Use your arrow keys to navigate among keys, since your mouse probably will not work in BIOS. The BIOS will greatly differ among manufacturers, so there is no one particular menu to select, which means you might have to do some exploring. Start with menu entries that mention "monitor," "performance," "overclocking" or "maintenance."
When you navigate to a menu item, you should see the available options under, or to the right of, the menu. Some BIOS menus might require you to press Enter to select them before you can see the options. You know you are in the right place when you see entries for "fan control."
Navigate with your arrow keys to select the entry, or entries, for "fan control." Press Enter to adjust the settings. Some BIOS will list a header, such as "CPU fan control" or "System Fan Control," with subcategories beneath. If you see "Disabled" next to the main header, then select the header and press Enter to change it to "Enabled." This will allow you to navigate below the header to adjust individual settings.
Move to the individual setting you desire to change and press Enter. Using your arrow keys, you can select your new settings and press Enter to accept it. The options you can select will vary widely among manufacturers. Some offer the ability to select precise speeds, voltages or temperature settings. Others might only offer the options of full speed or variable rates, which lets the computer decide the fan speed based on temperature; your motherboard might display no options at all.
Press ESC or F10 to exit BIOS and opt to save your settings. You will then exit BIOS and reboot with your new settings.