Hi
Is this in the preview or in the exported project?
Check the slider at the left end of the audio track..Has it been moved to the left? (0% volume)
Check the volume of the audio clip (Click the loudspeaker icon under the clip) ....Is it set to100% (or above zero)? If it was set at 0% it would not effect the slider position which could still be set to the right.
Check the speaker icon is not red crossed (muted) if so re-click it to un-mute it.
Check that an upper audio track has not been set to Solo.....(it would show a single "pawn" instead of a group of "pawns" This would mute all other tracks.
Nat