I was confused then... there are times that when I am playing heavy graphics games in my pc for several hours it suddenly hangs up or freeze and no matter what I do I couldn't move anything even could not move the mouse pointer. Then I have no choice but to press the re-set button... but the problem is... it didn't start up or re-boot like before..and nothing happens in the monitor everything is black.. but still the lights on my pc tower casing was still flashing. Then I just turn off the UPS and unplug the power source, and after several hours of "rest" I try starting it and it starts. It happens several times already, not only when playing games... but also there at one time I am scanning w MS AntiSpyware.. it also hangs and didn't finish the scanning process. What's the possible cause of this?