HP Envy 15 Screen Blank

Jul 2, 2018
Last night my laptop worked well but now the screen wont turn on. I've tested it with an external monitor and it displays there but not on the laptop screen. I'm thinking I damaged the LCD cable or something similar during my car ride home this afternoon. I was hoping someone would have some way I could troubleshoot or confirm that something along those lines is my problem. It's pretty late where I am but I'll try to answer any questions before I need to get some sleep. Thank you for any help.
Edit: The laptop works well connected to the external monitor. No flashing lights out of the ordinary or beeping on startup.
You need to take it apart and re-seat the screen cables. If that does not work, may be an issue with the screen or backlight. If it's in warranty, contact HP support.