Try starting the phone in "Safe Mode" and see if the same thing occurs. If it doesn't, then you probably have something on the device that is causing the issue. Bad app, or other software. You would then need to find what is the cause and then try running the phone in normal mode again.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.