Hi,
You need to hard reset your phone.
Before you do this make sure that the battery is fully charged.
'''Warning : A hard reset will restore your phone to factory default. You will lose all downloaded apps and user data!'''
To perform a hard reset do the following:
1.Turn off your phone
2. Press and hold the Volume Up + Power button (both together) until you see Recovery mode.
3. Select option "wipe data/factory reset" from the menu.
(To scroll options use Volume buttons, and to ''confirm press Volume Up key for 3 seconds'').
4. Then confirm "yes" by Volume Up.
5. In the end accept (confirm with Volume Up key) operation "reboot system now"
The phone should now reset, be patient it takes a few minutes.