Screen replacement now wont display image.

I had a customer come in with a samsung galaxy s7 that had a cracked screen and the screen didn't dislay an image. You could still see the lights for the back and the other button as well as the blue light in the top left hand corner and you could hear phone calls and notifications. So just like the previous 500 s7 lcds I have done I told her it was a bad lcd. Well now I put the new lcd on the device and nothing. I try to power it on and nothing happens not even the blue light comes on. I have to put it on the charger and wait for about 30 seconds for the blue light to come on. Can someone please help me out I would very much appreciate it thank you!

***Update - I Just had it on the charger and tried pressing and holding the volume down and power button for 30 seconds and I heard the att sound go off but still no image??