Why is my screen suddenly became blank?

Just a while ago my screen became blank. The phone looks shut off but its not. I can still hear it when charging and vibrates when i use the mute and unmute.

i restarted it by pressing the home together with the sleep/lock button for 10 seconds but it still wont open up and i can still hear the sounds as i charge it and vibrates when using the mute and unmute.

so i guess the phone is working well except for the screen.

I opened my phone and check the connections and its all fitted well and i didnt see any damaged cables.