1. Please enter the service EM mode to run the MMI test first to ensure is not the HW issue.
2. If it is not caused by hardware issue, re-download the device to latest SW version, and ask user to use the default factory setting around 3 days (don’t DL any 3rd party App(s) in the market) to see if the symptom is still exists. Most of the device problems that user complain about are caused by the bad quality or illegal Apps that downloaded by user, instead of the device itself.