If the power supply device fan works properly, computer overheating is usually due to dust accumulation. To withdraw this dust you may use your domestic floor vacuum cleaner, as follows: 1.- Switch off your computer. 2.- If you use a desktop remove the covers of the mainboard space and apply the tip of the suction hose to every place where dust accumulation is seen and also to the back side of the power supply, so that all the dust is sucked. 4.- If your computer is a laptop you only need to apply the tip of the suction hose to each and every hole at the bottom of it. The reduced dimensions of the inner space considerably increases the strength of the air vacuum. HTH