System recovery
If you forget your unlock sequence and backup PIN, you’ll have to perform a hard reset to gain access to your phone.
Performing a hard 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.
Read ALL steps before attempting.
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 
.Release both of the key when the System recovery screen is displayed.
Press either of the Volume Keys
to highlight Factory data reset, then press the Power/Lock
Key .NOTEHighlight Continue Power on to simply restart your phone without performing a hard reset.
The Factory data reset screen is displayed. Press either of the Volume Keys
to highlight Yes (or No to exit), then press
the Power/Lock Key to continue.Your phone will perform a hard reset and erase all of your personal data.