update to the latest Firmware and perform a factory reset in recovery after that.
wipe data/factory reset in recovery (this will delete your data/settings):
- Power off and then press Power and Volume up together for around 10 Seconds
- be sure that the little arrow point on recovery (select with volume up, enter with volume down)
- Then the open android with red triangle+"no command" is shown press Power and Volume up together again
- Select Wipe data/factory reset with volume keys, confirm with power
- After factory reset select reboot system now
Please report if this solved your issue or not.