Why no display on screen

What I would do in this situation is take off the back, disconnect the battery and see if it boots up, If that doesn't work then I would take out the memory and replace it with known working memory and see if it works. I have seen this previously and sometimes the Ram just needs to be reseated or replaced in most cases. If it turns on but still doesn't display. Connect it to the external monitor or tv. If it displays with no issues then your screen is bad. If it doesn't display then you possibly could have a board issue.