Have you try using another earpiece to test whether you can hear any sound. Just to clarify, is it the audio port that is causing the sound problem? If it is, go to your device manager and see if there is any problem with your sound driver. If there is a problem, there will be a yellow exclamation mark or red X beside the driver name.
Have you tried updating the sound driver recently? It could be a problem of driver compatibility, else as jingda mentioned, try another earpiece/speakers to see what it gives. In case of updates, try rollback to the previous version
have you used any other sound system like skype? Sometimes programs hog the sound system and do not return it to windows OS for other sound use. a reboot normally clears this but you may need to select your sound input device in the sound system. M