its more than likely hardware. And in further detail, it is probably your power supply. If not your powersupply it could be a wiring problem.
possible fixes:
1) replace the power supply (dont do this first)
2) rewire your whole system (look at your mobo manual if you have to)
3) make sure that you are plugging all required power supply connecters to devices and make sure they are snug, not loose.