Have you tried this?

There are a few things you should try first when you experience problems with your device:

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  Restart

  Restart your phone to turn off all running applications and to free up memory. Press and hold down both the volume up key and the power key for 10 seconds. After your device vibrates three times, release the keys. The device turns off automatically. After the device is turned off, restart your phone.

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  Update

  Update your phone to ensure that you have optimal performance and the latest enhancements. Read more about how to update and find latest software version.

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  Reset

  Reset your phone to its original settings to remove memory blocks: Settings > Backup & reset > Factory data reset > Reset phone Don't forget to back up any important data saved on your phone!