If you have the possibility of audio via HDMI, then this will have precedence over the onboard audio solution and be selected by default. In order to change this ordering, you need to go into the Windows Mixer and change the default audio output solution to be the RealTek audio solution. To do this, right-click on the Audio icon in the system tray and select Playback Devices (on Windows 10, select Open Sound Settings). In the dialog box that appears, find the entry for the RealTek audio output desired (typically Speakers), right-click on its icon and select Set as Default Device. (on Windows 10, select the right entry in the Choose your output device box).
Hope this helps,