That's a hard one to nail down ...
Could be the power supply .
Bios update might cure it .
Could be a component is not initially reading correctly , I had a video card cause the cold boot problem before and some memory caused it before as well .
I read that setting the bios to let the long boot up process ( long memory count ) is best but recently had a board that sometimes hangs in the long boot-up but will boot everytime with the long boot-up disabled , short time boot-up is fine .
That is my experience with that problem , I'm sure there could be other variables that could cause it , like a surge protector or something .
Good Luck .