Default screen gone wild

my wife's s4 mini (completely stock) has developed a fault where when u press the screen it will press in several other places also.
the phone has a slight scratch on the screen, so this is what I thought the problem was. this morning however it froze so my wife restarted it, when I came back on it said there were 3 messages and there wasn't any when she checked.
it had also changed the time and date.

can anybody give their ideas on this please