My HP Pavilion laptop is about 2 yrs old. a few months ago, it let out a high pitch sound for no reason. the screen went white and slowly got darker until i could see a black screen behind several colored vertical lines. I shut the computer down and started it up again, but the screen was white and slowly became the black screen with the lines. i don't remember dropping, spilling, or downloading anything onto it. i've tried the fn thing and hard reboots but nothing helps.
This sounds like a hardware problem with the backlight system. Most likely with the "inverter". The good thing is inverters a relatively easy for a technician to replace. (it's not user serviceable). I would find a good PC repair shop to do the job.