I had a weird issue similar to this over the weekend. One minute my phone was fine then the next minute I tried to wake it and the screen wouldnt come on. I even held the power button down (to turn on or off) and nothign was happening. I was like "W....T....F......?!?!" I was pretty nervous as I LOVE this phone. I couldnt think of anything to do and I couldnt plug it into a PC or charger since I was at a bar with some mates. Long story short...after a few attemps to just keep pressing the power button down lol it finally started up from a reboot.
Very weird indeed....everything has been fine since and I am running stock.