It seems to be fairly common for the circuit board on the inside to move around a tiny bit, and even if you are pressing the button down all the way, but at a certain angle or something the button will cut out. If it does this several times in a row, like someone else said you could get into the menu and change the power settings.
This has also happened to me a few times, and without lifting the button at all. I then went about trying to get the button to cut out while still holding it down, and it seems to cut out often if I put downward (towards the bottom of the
device) pressure on the button while I'm depressing it.