I am having a weird version of this pretty well known problem. This is an HP Pavillion DV9520 laptop running Vista (it is not part of the recall from HP - but maybe it should be). From power-on, the screen is dead, absolute black. No HP, BIOS screen or the like. However, the machine is booting, the disks start and if I attach an external monitor the whole proper boot sequence can be seen (HP welcome screen, Vista login, Vista desktop). I have tried all the known fixes for this including reseating RAM, removing battery and holding power switch for 60 seconds, etc. I even tried popping out the backup battery. All to no avail.
I have found something that works fairly consistantly. If I attach an external monitor and leave the laptop lid open at about 30 degrees, the laptop screen works. I see the Microsoft moving bars on the laptop. However, when the Vista login screen comes up, the laptop goes dark and the external monitor (only) displays the Vista login screen. Once I enter my password (without lifting the lid from its 30 degree position) the laptop screen comes back on and I see the desktop on both screens.
I have not tried holding my mouth a certain way when I boot or getting up and walking around my chair twice but am willing to try if anyone thinks that will work. I would really appreciate any other ideas you have as well.