I have a Intel Celeron D 2.4 Processor, 512 DDR 333Mhz RAM, ASRock MotherBoard, 300Watts Power Supply. All the things were working fine a few days back now the system has started to shutdown at irregular intervals of time. This cant be any virus as i am using MCafee v9 and that is updated i have scaned my system several times but found no virus. I also have scanned the system for adware from LAVA SOFT ADAWARE found nothing suspecious. No new hardware is added. I have attached a chasis fan as i was suspecting a heat problem but the problem still remains. I have checked the power supply and that seems to be fine to but the system still shutsdown after 3 ~ 4 hours of operation and then i have to restart the system by pressing the power button.