I have a weird issue where the LCD of a Dell Precision M6400 laptop is 100% working but only in Windows. It won't display the BIOS or the Windows startup process even with the external monitor disconnected. When turned on the LCD will display a blinking cursor then go dark during the boot process and only come back to life at Windows login screen. I've tried using the Function key plus the F key for the display selection but that doesn't do anything. I mean the display options come up on the screen in Windows but it won't switch between monitors, expand, etc..
I have a feeling that maybe whatever switch or sensor that detects the LCD lid is open/close might be the issue but I don't know how to fix that or where that is. There's no mention of it in the service manual for this model. I don't know if it's related but the keyboard backlight is also not working. Everything else is fine.
Has anyone encountered a similar issue? The laptop passes all diagnostics (Dell and third party) I throw at it.