Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, was there a recent update downloaded/installed?
If a factory data reset was not corrective, then it would be an internal hardware issue.
Consider removing the battery (if have not been done) for an extended period of time. Please click HERE. This would serve as both an attempt of a fix and as a test by process of elimination.
If a hard reset (battery removal) was not corrective nor was the factory data reset, then it would confirm the internal hardware issue. The LG would be needing repairs or replacement.