Booting or screen problems? Any solutions?

Not sure what is wrong with it but I can get it to boot to an external display in safe mode by pressing the shift button and the power button. If you try and power up without hit shift key it gets stuck. The MacBook screen does not turn on, it will flicker on boot up. Once it powers up the external screen flickers and from there I am able to update software, connect to internet ect. I was even able to reformat back to new computer mode