1
Open the Settings App.
Go to Update and Security - Troubleshoot
In there, run the Playing and Recording audio troubleshooters.
Restart your system to see if that resolves the problem.
2
If that does not resolve the problem, go to the support page for your PC on the manufacturers website, then from there, download and re-install (not update) the version of Realtek HD Audio drivers they provide for your system model.