If you know for certain that the battery is OK (externally load checked) and that the power unit is also operational then it could suggest that an internal fuse has blown, that is excluding a fault being present on the power input socket which generally has internal changeover contacts which can oxidize and cause a severe voltage drop. As a model I do not have the service info for as a rough guide camcorder fuses are nearly always located inside the rear casing close to where the battery is located, and these are nearly always of the special miniature soldered in types although there are some cap ended miniature types about that can be carefully adapted to suit.