Hey Guys,
This happened to me as well and I got it working again.
I went to bed and when I woke up I turned my phone on but the unlock screen was unresponsive. I pressed and held the power button and I felt it vibrate which normally happens when you are presented with the power down options, however nothing came on the screen, it was still at the lock slider. So I did a battery pull, reset it, checked a web page and then went back to bed. When I woke up again, there was nothing but a black screen and pressing the power button did nothing.
I figured maybe the battery had fully discharged. I plugged it into the wall with the supplied charger for a few minutes, nothing. Plugged it into the computer with the supplied USB cable, nothing. Plugged it into the wall using my Blackberry charger, nothing. Tried doing all of the volume + power button combos while plugged in, nothing. Tried battery pull and still nothing.
To get it working again I unplugged it from the USB and then took out battery and the SIM card. While the battery and SIM were out I held the power button down for 10 seconds, thinking that there might be some built up power/static that needed to be discharged. I replaced the SIM card and battery and as soon as I plugged the USB cable in, the battery charging symbol appeared. Left it for a few minutes and then pressed power and voila, it was back.
Now, as I said before I thought that maybe the battery had fully discharged... However upon powering up my battery was at 45% Very weird.
Anyways, that's my story. Maybe my idea of holding the power button with the battery and SIM card out had an effect, maybe not, I don't know. But if you find yourself in this situation I'd say that it's worth a shot.