In order to fix the issue, go to Start, type dxdiag and open the utility. Click the Sound tab, check your audio card model and download and install the latest drivers available from the developer's web page. After that, right-click the sound icon from System tray and select Playback devices. Right-click anywhere in the Playback window and check the Show Disabled Devices option. Select your sound device, press the Set Default button and then click Properties. Choose Use this device (Enable) as Device usage, click Apply and then OK. Reboot your computer and try again.
If it doesn't work, press Windows + R key combination, type devmgmt.msc and click OK. Look for your TV tuner driver, right-click on its icon and select Uninstall. After that, navigate to the official web page and download and install the latest drivers and software for Mercury TV Tuner Card.