So I have a 15" MBP with a cracked screen. when its powered on the screen is lit, but nothing on the screen is showing. I bought a replacement screen. I took the MBP apart carefully and installed the new screen. its all put back together, I power it up and the screen stays off. I know the MBP is on because I plugged it in to an external monitor. I took it apart again to make sure I didn't have any loose connectors. Put it all back together and same thing. Does anyone have any ideas. thanks.