The display on my Compaq Presario f750us doesn't turn on. I connect to an external monitor and everything works fine. This problem has been there for sometime now. But the display used to turn on after folding the monitor to different positions (don't know why that worked). Only yesterday I couldn't get it turn on how much ever I tried. I can't get the display to turn on since.
Please note that the display worked fine after it turned on.
Sounds like either your LCD or inverter (or both) are bad. Could also be the sensor that lets your computer detect if the lid is closed is worn. Older notebooks had this sensor as a simple switch sticking out of the keyboard deck, but I honestly don't know where they are on newer notebooks.
I have the same problem with an HP 2810US. External monitor is fine but LCD display is not recognized and is black. The Fn-F4 function does not work although it causes the external monitor to briefly flicker when I try to toggle. When I look at any of the system functions/menus the LCD display does not appear or is not recognized as an option.