It could be your cpu or videocard is shutting down the computer to prevent it from overheating, do you have adequate cooling (most motherboards come with a utility to tell you the temperature of various components of your computer)
if u wana see if your system is alive but you just cant see it press alt-shift-num lock if you hear a sound it means that the black screen in only in VGA and screen
if u wana see if your system is alive but you just cant see it press alt-shift-num lock if you hear a sound it means that the black screen in only in VGA and screen
about the problem may i suggest you to check your RAMS for errors because my pc restarted from that long time ago
