Hi,
Unless the laptop's video cable has become disconnected from the motherboard or from the display panel itself, you'll have to replace the display.
Here is a link to the [http://h10032.www1.hp.com/ctg/Manual/c02829479|service manual] for your laptop.
Scroll to p.62 to view the necessary pre-requisite steps and then the procedure to remove the display assembly. Unfortunately you nearly have to completely remove the display panel to check the video cable connection on the panel
Also on p.62 you'll find the display part numbers appropriate to the various models, if it seems that there is no problem with the cable connections and you have to get a new panel.
Use the part number ''only'' in the browser search box, when you search online to find suppliers of the part.
Hopefully this is of some help.