HP Laptop Battery problem

Question

I have an HP Pavillion latop DV9000. The batter is no longer recognized by the laptop as even being there. I bought a new battery assuming that was the problem. Still did not work.. My friend as exactly the same laptop so I took his battery out and installed it fully charged and the laptop still did not even power up. It will work just fine when plugged into the power from the wall and even display correct icon that it is plugged in. So it appears the laptop does not get any power from the battery. Suggestions? THanks