I have a 2 year old Samsung Galaxy S4 tablet. Last week it t began to freeze on a particular page as I was reading. Shaking and tapping roughly on the screen causes it to unfreeze. Each day the freezing happens more frequently. I am concerned that it will totally freeze when I am in the middle of an exciting part of the story or will cause me to lose all my ebooks. What causes the freeze and can it be fixed? Thank you for your help. Patti Guerrero