When the screen is cracked, broken or faulty you notice flowing problems:
> brightness flickering
> screen appearing extremely dim
> reddish tint on the display, specially on the bottom,
> display going off after couple of seconds (can also be caused by video chip fault on the motherboard)
> white patches present on the display regardless of displayed content
> pixel thin vertical lines across the display
> black lines appearing on the screen and getting thicker or spread more when you touch them