LCD screen is not turning on, but phone is On

Hello, I had a problem before with my battery and lcd screen, the battery was really used. but first I buyed a fresh screen for the phone, I used it with the bad battery and the screen went on perfectely. But after one day it didn't worked anymore cause I thinked that the problem was the battery, not the screen because it was new. But now that I got fresh battery, the phone turns on and everything but the screen remains BLACK. I just don't know why! Tried everything! Restarting, disconnecting the screen and connecting again, nothing works. And yea, my power button is broken, I can only turn on the phone by usb. I don't know what to do, please help me. The phone turns on, with black screen, and keeps beeping that it is charging...no idea..:/