How do I stop my phone from constantly restarting?

[AC Question]

I have a new LG G4 phone from Android, and it's not even 6 months old, but it keeps restarting. The LG logo will come up, then the screen will go black, and then the LG logo will appear back up. It's been doing this for about 5 hours now, and I've tried resetting it back to the factory settings, but it goes right back to rebooting on it's own. Do I need to take it back to the provider and get it looked at?

 

[Sjalabaisen]

With my phone, it was the nano-SIM that had broken out of it's micro-SIM hold - it was moving. A bit of tape fixed that.