IF it's available in your specific versions, go to the Control Panel/Hardware and Sound/Sound. In the Sound Panel click on the "Recording" tab. If the System Mixer is shown, Right Click on it and Select "Set as default device". If it is NOT shown, RIGHT click in an empty space on the panel and then LEFT click on "Show Disabled Devices". If this does not show the System Mixer it means the System Mixer is not available in your RealTek driver
. Check with the PC or motherboard vendor to see if there is an updated driver.