Do other input devices connected to the laptop work (for example, a USB keyboard and USB mouse)?
If an external USB keyboard works, then the next thing I would do is check to make sure that the internal keyboard is properly connected to the motherboard. This will require you to do some unscrewing, but it's pretty straight forward. The Maintenance and Service Guide for the HP Paviliion zv5000 Notebook will tell you how to remove the keyboard, and what the part number of the keyboard is: http://h10032.www1.hp.com/ctg/Manual/c00212209.pdf
. Follow the instructions to remove the keyboard on p139.
If it is properly connected, then I would think about replacing the keyboard.