Hold down the power button for at least 10 seconds. If that doesn't work, remove and then replace the battery. Good luck!
Sounds like the phone is downloading a system (OS) update.
Powering off the phone could potentially corrupt the update.
I was listening to music this morning, and I went to shut off my phone to check something, I am not sure what, and when I shut it off, this message popped up as soon as my phone was off. WTH!? I have had this phone for less than 24 hours. I have browse through the manuals and have seen NOTHING. So could someone PLEASE tell me what the hell is going on with my phone. THANKS!!!
I'm guessing you had the USB cable hooked up to a computer at the time? If the phone is turned off, and it is connected to a live USB connection, holding the 'vol down' will put it into 'download' mode. This is where emergency firmware fixes can be done.
If that's what happened, just unplug the phone and take the battery out. Put the battery back in and you are good to go.