I would remove all the power from the computer, ac adapter and battery, hold the power button in for 30 seconds then reconnect it to see if that resets it. Would try removing the ram etc.. to see if something is causing it not to post. Some of the HP DV 9000 Models did have an issue with the Nvidia Graphics chip as well.
http://www.nvidiasettlement.com/affectedmodels.html
Nvidia in a settlement is replacing certain units that experience video problems, not sure if you were having issues with that previously but it is worth looking into.