You could have broken anything and everything in there. It is no surprise it would not boot up. Please do NOT try to force it to power on anymore, because you can only make things worse by adding power to it. Take it to a repair shop or call up HP for assistance.
almost without a doubt you have "broken" your hdd.it doesnt take much of a fall to take out a hard drive.try booting to the bios and see if the hdd is recognized there.
With the caveat that if your data is mission critical, you should cease using the system AT ALL, and bring it to licensed recovery specialists. Once a hard drive is dying or the filesystem gets overwritten, all you do with further use is generally compound your problems.
That clicking head could be the motor, or it could be surface damage on the hard drive - if it's the latter, using it will just make the data harder to recover, should that be within the realm of consideration.