What model is it? I had this happen to an HP dv9005 and my wife’s Compaq F500. Both machines were out of warranty, but HP had issued a service bulletin authorizing free repair to both models. Turns out that the fan algorithm in the bios was incorrect and the resulting lack of proper cooling cooked components on the motherboard—at least that’s what HP said. The problems started on the DV about a year after I bought it: First the screen hinges cracked, then the card reader died, then the wireless died and finally the video card fried, resulting in the black screen you also seem to have. The upshot is that HP fixed both machines for free, including the shipping, and I haven’t had problems with either since. The DV was returned to me in December, the other one about three months ago. Both now run fine, and both run a lot cooler. Check the HP website for the repair bulletin. First time(s) I ever had problems with HP products, and I’ve bought nothing but for eight years.
Oh yeah, and the cure was new mobos for both.