Blank white lcd

Yes, it could very well be a dead LCD unit. I have a LCD in a laptop in the office that has a nasty line running down through the entire screen. We contacted someone about replacing just the LCD portion of it and they said - don't bother. They said it would be more prudent to wait until it dies, and then upgrade to a new computer. It is the nature of the LCD units themselves, when they give up the ghost they give up the ghost.

The fact that you can see everything fine on an external monitor shows that you have lost your LCD. The odds of the cable inside the machine going bad are minimal/tiny to say the least. If they were exposed cables such that they could get crimped, then possibly that could be the culprit. With them being routed inside the unit, it is almost impossible for them to get pinched.

The only other option, and this only works if your machine is still under warranty, is to have HP fix it as part of your machines warranty. BUT, not all warranties cover the screen anyhow. The laptops I have bought required me to purchase insurance on the screen itself.

So, you'll have to determine if you can manage with the external monitor all the time or if you need a new laptop.
Sorry it is not good news for you.