I had the exact same issue except this was happened during the boot up after the initial software update.
I got so excited when I first got the thing that I didn't bother charging it first. I just proceeded with the setup.
After almost 3 hours of messing with it (rebooting, holding the volume down and power button) it still would not finish with the boot screen. I called Blackberry technical support and they had me plug it into the wall charger. After about 30 minutes the dancing lights went away by themselves and brought me back to the wi-fi setup screen and gave me a message about it not being able to connect.
I had it plugged into my computer via USB for about an hour but I guess it just wasnt providing it enough juice.