First at all, try to plug your phone into the charger. If it doesn’t turn on and begin to charge within a couple of minutes, the battery may be dead. If the battery is dead, it will need to be replaced with a new battery.
Second, if the problem persist, it is possible that the phone is turned on, but the display isn’t functioning properly. The backlight or the LCD will need to be replaced.
If the phone still not on, the problem is probably that the logic board is bad and needs to be replaced.