This is what happened this morning. For no good reason at all, the phone was off completely when I went back to it. I know I made a call earlier in the morning.
- Normally off-phones can be turned on by pressing the power button for 5-10 seconds. This time, it did not respond.
- Normally if it is completely out of battery, it will also show some charging sign when it is plugged into the charger. This time, that did not happen.
- I left it on the charging stand thinking that at some time the battery charging sign would come on. It never did.
Try holding the big square "home" button in the bottom middle of the phone and power button pressed together for good 30 seconds or longer, and it worked for me.
This never happened to my iPhone 4 for the entire 3 or so years I owned it. I upgraded it to OS 6 recently, that may have something to do with it, and it might happen again because of this. If so I will post again if this tends to happen a lot now. Also ironically, it just happened at the time I was several weeks (looks like some delay) before my iPhone 5 arrives. If it was completely dead, I am certainly in a big bind, and may be forced to move to an Android phone.