What brand is your power supply and have you tested it lately?
I had major problems lately with Antec power supplies combined with ASUS motherboards...
You might want to try swapping out with a different power supply, something such as a Cooler Master, Seasonic, or another good quality name brand.
I've had this error many times with ASUS boards and Antec power supplies until I stopped using Antec totally.
Try replacing the power supply and hopefully your problems will go away...