Hi, Sorry to hear your having this problem to help you I will be telling you how to perform a "hard reset" you will keep all your data and contacts.
1.Press and hold the Volume down button, then briefly press the Power button. Keep the volume down button held down until an icon appears.
2.Press Volume up.
3.Press Volume down.
4.Press Power.
5.Press Volume down.
6.The phone will reset and reboot to the initial setup screen