With the info you gave us here is what I can get you to try,
1 Make sure you don't have anything clogging your ears.
2. Are you in the same room as the PC, maybe you are too far away to hear it?
3. Do you have speakers and are they turned on?
If you need any other help you may want to provide your computer model, when the sound issue happened, what you tried to do to fix it already.