Unfortunately all suggestions require physical access to the camera because it's very difficult to determine what happened. If it's in wireless mode, it would be more susceptible to disconnection due to the nature of the technology especially if it's placed far from the router. It may just need a reboot to re-establish connectivity. There is little you can do remotely but once you do have physical access this is what I would do.
- Reboot the camera and verify that the green LED comes on and then try connecting again
- Connect camera temporarily (if it was in wireless mode) to router, reset camera and reconfigure and rebind to mydlink
- If this does not work then I would get in contact with D-Link in your country of residence for additional support.