Your PC shuts down by itself! Remove the cover and feel the heat sink below the fan. If it feels extremely hot then your fan is not properly cooling the cpu. Replace the fan with a strong one powered directly by the power supply and NOT the motherboard. The PC protects the cpu from permanent heat dammage by shutting itself off! Also check the fan is turning in the power supply. Excessive dust in the fan can cause it to malfunction. chris drpcdr.ca