I currently have a Dell Inspiron 7559 that will boot up with no issues but the laptop screen does not display anything and is black. I have attached an external montior and that works perfectly.
Since I narrowed that down I then figured it was either the video cable from the mobo to the screen or the screen itself. I have replaced both the cable and screen and still am only getting a black screen.
I am out of suggestions and things to try to get this issue resolved. Any help is much appreciated.
I am assuming here that you replaced them with the exact same parts? Not alternates or aftermarket ones. If that is the case, then it could be a flawed new part. Less likely but still possible. I would suggest returning said parts and get alternates so you can make sure it isn't the parts.
That said, before proceeding, take a small flashlight and aim it at the display (at different angles). Do you see anything at all? If you do, then it is likely an inverter that is bad and not the display or cable. If that is the case you will have to replace the inverter.
However, if you see nothing, then we are back to either the parts you replaced are the wrong ones or are bad themselves or your external monitor and attached display are using different graphics (like one using the integrated graphics and one another GPU).