Some sound cards have a Karaoke function and remove all voices, maybe this is what's going on here. In the Windows task bar, right-click on your sound icon and go to the properties for your speaker/headphone and make sure this setting is not turned on. If you have installed an external audio program like the Realtek Audio Manager, also make sure to check those settings.
This could also be a different problem so let us know if this didn't work so we can try something else.
