|Factory Reset usually fixes that, but keep in mind that a Factory Reset will delete all user data on the phone. Files on the SD card won't be affected.|
To perform Factory Reset:
1 ) With the phone turned off, press and hold the VOLUME DOWN button, and then briefly press the POWER button.
2 ) Wait for the screen with the three Android images to appear, and then release the VOLUME DOWN button..
3 ) Press VOLUME DOWN to select CLEAR STORAGE, and then press POWER.
4 ) Press VOLUME UP to start the factory reset.