My LG Optimus G keeps rebooting. When it starts up, it never recognizes the ATT network, or even the phone number that it is registered to. At one point, I did a factory reset, and it restarted a few more times, and it started working. Now, about 2 weeks later, I can not get it to stay on. It only stays on for 20 to 30 seconds, just enough time to search for something in the settings. The phone is maybe a month old, as it was an insurance replacement for another phone. Any suggestions?