Pan is the balance between your left and right speaker.
If you only have 1 speaker, you have no stereo options. In this case, when the pan is set to only be shown on the left speaker, the right speaker will be silent. If your left speaker is disconnected or nonexcisting, then you will hear nothing.
If you have stereo speakers, make sure they both work. If you only have 1 speaker, set your OS audio to mono.