first at all you have to update the bios from the website of hp second the if the laptop as you said is shown in external screen thats good thing coz you are sure for now that graphic card is ok third you have to test screen with another one no need to be same size just for testing if not working you need to test the spin between screen and laptop you screen is led as i assume it doesnt have inverter then leave comment
start by login bios check if the usb are disabled then try to do resotre your windows to date that work fine if nothing happen you must pull out the motherboard and do the voltage test
download hirens boot 10.7 boot from cd you will see password tools press you will get active password changer then choose the driver then clock on password must change next login then press Y then restart when you get start screen just press enter twice
