Have you right clicked the speaker icon usually in the lower right screen corner?
There are many user controlled Playback and Recording settings - you may need to "drill down" in all of the various tabs and property options that can be configured.
Also check any and all cables that you may be using. Ensure that the connections are all snug and tight. Swap in known working cables if you can.
You might need to update and reinstall your sound card drivers.
If none of that proves successful, please post some additional details about your setup and configuration. Thanks.