I dropped my HP laptop with the power cord in.

Now when I push the power button all I hear are three clicks and nothing.

What are the possible problems?:
Something came loose
Hard drive was shocked

etc...

Was it on when you dropped it?
Was the case damaged anywhere?
If it was turned on, the hard drive was likely damaged, but you may still be able to recovery your data using a USB external drive.

One step at a time: with the power adapter removed, remove the case covers for memory, and hard drive.
Remove and replace every cable. Remove and reseat the memory modules. Remove and reseat the hard drive.
Remove the keyboard... Usually by removing 6 to 11 screws from the bottom, and two to five from the top.
With the keyboard removed, tip it upside down over a nice large sheet of white paper... like a poster paper or cardboard... look for chips, particles, plastic, black, green, or golden... any particles may indicate your motherboard has been damaged.
With the keyboard off, look for a wide, thin ribbon cable that is 1 to 1 3/4 inches wide. Remove and reseat that cable.
Look for an odd-shaped batter on a set of cables... red and black, green and white, green and yellow. Look for any wires unplugged.
You might want to invest in a new hard drive... depending on where you live, they may run from $44 to $88. You will always use it later when your regular hard drive wears out... assuming you fix it now.

Then get back to us.

Hard drive damage gets my vote

Thanks Everyone!!! I disconnected and reconnected everything and now I am up and running. But I have backed up everything to my external HD. I think in the big scheme of things I was more worried about losing all my information and documents than I was about possibly buying a new laptop.