System recovery
If you forget your unlock sequence and backup PIN, you’ll have to perform a Factory data reset on System recovery menu to gain access to your phone.
Performing a Factory data reset deletes all of your user data, which includes pictures, videos, and music saved to your internal memory. Please make sure to back up your information prior to performing a hard reset.
Turn the phone off.
Press and hold the following keys (on the back of the phone) at the same time: Volume Down Key
+ Power/Lock
Key 
for approximately 10 seconds.Release both of the keys when the System recovery screen is displayed.
The following options are displayed: Continue Power up, Safe mode, USB debug mode, Factory data reset, Wipe cache, and Power down. Press a Volume Key
to
scroll to the desired option, then press the Power/Lock
Key to confirm.NOTEHighlight Continue Power up to simply restart your phone without performing a hard reset.
Choose Factory data reset, press either of the Volume Keys
(on the Factory data reset
screen) to highlight Yes, (or No to exit) then press the Power/Lock Key (on the back of the
phone) to confirm.Your phone will perform a hard reset and erase all personal data from the phone's memory.