my ipPhone (4) started vibrating and when attemtpted to answer what thought was call nothing happened. Screen completely blank cannot turn phone on ar off screen remains blank and cannot charge it either. tried to take sim card out

my ipPhone (4) started vibrating, and when I attemtpted to answer what I thought was an incoming call, nothing happened. Screen completely blank, cannot turn phone on, the screen remains blank, and cannot charge it, either. I triedtaking the sim card out and then putting it back, but that doesn't help either. Any ideas...?