Initially suspected was the powerpack's fan. Replaced that.
Took off computer cover. Run the computer in an aircond room with a tablefan blowing at it. Still the same. It stills reboot randomly with no apparent reason. No BSOD (Blue Screen of Death), just reboots.

This random rebooting, well you can do two things for now,

1. Power up the pc and let it stand for a while, see if it reboots on its own without your inter-action.

2. Test the system with the utility that you should have had with the mobo, look for any signes of over heating and voltage movement,

anotherthing is that one of the components may be malfunctioning on the mobo. I have heard of compononts which are plugged into the mobo instead of being soldered, creeping out of their locations.

Look over the mobo for any signs of over heating/chips not set into their connectors correctly and also conduct a heat test on the motherboards components, also strip the pc down from all of its pci cards except any graphics cards, set the bios to defaults then try the system