Since you didn't say that you don't have volume muted:
Check the "mute status" either
- in top menu > Player > Playback Options > Volume
- or by right-clicking the volume slider
- or by clicking the small speaker icon besides the volume slider
If that wasn't the cause of the problem could you check what you have set in the playback options and also test if different settings would work?
Did you notice the problem after installing a new MC build or something else on your PC (like Windows updates) or did the audio output just disappear even though nothing was installed or any settings were changed in MC or Windows?
Also, you didn't tell what kind of files you have tried to play, but based on your description I assume you cannot hear any audio output - no matter what file or media type you try to play. Am I correct?