|If your system is under warranty I suggest call HP to sort it out .|
If out of warranty then open the case and locate the CMOS reset jumper. With power disconnected, place the jumper in the reset position and press power button. Return the jumper to the run position, reconnect power and see if it will start.
Option if you cannot locate the jumper is to remove the CMOS battery for 1 minute and re-insert. ( with power disconnected)
If it still will not boot then I'm afraid the bios has been damaged and motherboard replacement might be your only option.
Goin' Fishin' (Some day)