iPhone 4 Not Working

Hi, i have an iPhone 4 and its pretty cracked and it has been like 6 months, so a few hours ago i was playing a game and the iphone froze, so i tried to turn it off with the slider but it wouldnt appear but the assestive touch still was working, so i locked the phone because this usually happens but when i tried to unlock it again it would just not work, since my home button does not work i can now restart it, i can only use the lock button, but when i put my charger in the phone vibrates, but the screen wont work its just black is it broken?

Help please