Hi my name is ***** ***** I would love to help you with this. Is this a new unit? Did this problem just start happening? Any info would be helpful to give you a good answer.
It looks like this camera will work on 4 AA batteries, either NiMh or non-rechargeable, right? I assume you put new batteries that you know are good and that is what you mean by "change d/c battery".
If that's the case, likely either the camera has a failed component inside, or MORE likely there is corrosion build-up where the batteries connect. If you shine a flashlight into where you put the batteries and you see any buildup, that will prevent the batteries from making an electrical connection and would explain why the a/c works but not batteries.
Take a pencil eraser and rub the eraser on all of the battery contacts of your camera and on the battery terminals. It will make a better contact for the battery when everything is cleaned off eliminating oxidation.
If this answers your question, great and I'd appreciate it if you would rate me. Otherwise let me know if you need more help!