are you rooted?
Whether you are or not hold power and volume up this should take you to the bootloader menu, use the volume key to go through menu until you see recovery and hit power button to select. In recovery use volume key to navigate to wipe data/factory reset (this will wipe your device of all data) navigate to wipe cache , then navigate to reboot.
The reason I asked if you were rooted because a custom recovery will help protect media/data (pics, music, etc) and also if your recovery has not been updated that is most likely your cause for the issue.