Is the microphone sensitivity or audio input sensitivity set to [Microphone off]?
No sound is recorded with videos if [Microphone off] is selected for [Microphone sensitivity] or [Audio input sensitivity] in the video recording menu. Select [Auto] or [Manual] to record sound. Ensure that the microphone sensitivity is not set too low when [Manual] is selected.
Is the setting for [Audio input selection] appropriate?
If your camera is equipped with the [Audio input selection] item in the video recording menu, select [External mic] when connecting an external microphone and [Line] when connecting a sound mixer or other audio device via a line cable.
