Well my computer is also rebooting randomly. Since I have 3 hard drives and a 6400 amd cpu with a 400 watt power supply would I need a bigger supply?

That may be it... or you need better circulation inside the box. That's a lot of heat to disperse. For now, just take the side off your computer and see if that stops the rebooting, if it does you know it's just an overheating problem.