If you get nothing at all on the screen (no BIOS screen, no HP logo, nothing) then I would think that the screen is broken. Do you get any picture at all- a faint ghosting, if you look carefully? If ot is an older lappy (3/4 years or more) a broken screen would not be unlikely. there is an invetor unit that feeds the screen backlight, and these can often go. Best bet would be get a professional to lok at it- repairs on laptops are difficult to say the least if you have little or no experience, and a pro shop can usually tell you fairly quickly (and hopefully cheaply) where the fault lies- chances are that its probably a better bet (if its older) to go for a new model, as repairs can often be worth than the original is worth.