Wow. I left my iPhone 3GS on charging overnight connected to my computer. When I woke up, I came to my iPhone, and pressed the home button. It stayed off. I pressed the power button, it stayed off. I held the power button, a white screen came on. Whenever I press the sleep button, the white screen shuts off. And, I heard a new e-mail noise, so I "Slide To Unlock", even though it wasn't there. It made the unlock noise. So clearly, everything works, it's just that my screen is displaying a white screen instead of the correct screen. A sleep/home button hold reset it fine.