Just go to E-Bay and type in HP G62 Power Button
, and you will find a bunch of them for $20 to $30.
If it is the actual button, and it feels ok, but doesn't make contact, you may be able to take it apart. See if there is a frame that will snap off (carefully). Inside you should find a little diaphragm disk and a couple of contacts. See if you can clean it and put it back together.
It appears similar to the laptop mouse buttons that I have successfully cleaned in the past. Cleaning it might fix the button, but obviously not circuit board problems.