i have no motherborad manual it was a prefab computer. i know its the fan on the cpu because theres only 2 fans in the comp, and i held the fan at the back to stop it and the comp still made the noise when i turned it on while holding the fan.the noise that it is making is just the sound of the fans spining really fast. it used to spin fast when it was booted up then go nearly silent after about 10 seconds but now it just sounds like its spining that fast all the time. and thanks for taking the time to read my older posts.