| | This is how I got it to boot...
I had the same problem (big battery sign with light bolt), and this is how I got it to boot again.
1. While the BB was connected to the power wall, I removed the battery
2. I waited 30 seconds, you should see a red light during that time
3. I put the battery back, and then it rebooted back to the normal BB home screen. I noticed that the battery sign was red (AKA completely drain). By the way, if the BB does not come back after you put the battery back, and you wait a few seconds, just press the power button.
I'm going to wait a little bit and see if it charges completely.
I hope it helps.