after replacement was installed I have not got a picture

before I removed the broken screen I had picture after replacement was installed I have not got a picture. I checked all the connections and all were tight and still no picture.

I do have the sound of a message coming in but screen is black.

I have tried all the "Hold this and that button down for so long"

I'm not sure what to do now.Does someone knows what happened?

I badly needs help!

Best regards

Besty