I have the exact same problem. The phone doesn't even shut down properly, the screen just goes black and then it starts rebooting. I've tried removing the battery, I've tried changing random settings to see if I can interrupt the reboot loop. No luck. I've had this phone for all of one day...
IThis is a shot in the dark, but it would only take up a few minutes of your time.
For some owners of the LG env3, the restarting problem was resolved by cleaning the battery contacts with an eraser and putting up to a few pieces of paper between the battery and the battery door.
Recently our LG VX8700 that we've had for awhile was restarting repeatedly during this one day. And today our Motorola E815 also suddenly was repeatedly restarting. For both of these phones, I examined the battery contacts to look for any debris and I also put a few pieces of paper between the battery and the battery door. After doing this, neither phone has so far had a repeat bout of restarting. I am hoping that this is not a coincidence.
You device make be defective and if has only been one day since you purchased it can be exchanged for another new device. If the phone was purchased at a store you need to return the device to that store and have it exchanged. If it was purchased on-line or via Customer Service we can exchange it by calling 800-922-0204 or by replying to the private message we will be sending you shortly.