HELP!My iPhone4 is black but is still making sounds?

I have had my iphone for sometime now. about a year ago I think I may have pressed down to hard on the lock button and it got jammed down into the phone, so since then ive just been using the assistance touch. just yesterday I saw that the phone had 3% of battery left so I plugged it in and walked away, i come back about 10 mins later and I try to use it and the screen is black but when I unplug it and plug it in again it makes the sound when it starts charging. I search on google how to fix it but most of the solutions I cannot do since my lock button is broken!!! PLEASE HELP