The System Mixer, may also be called Stereo Mix or SoundBlaster calls it What You Hear. It is what is needed so that any input is heard on the PC speakers and also available for any recording program.
Apparently that is either not set or not available. Your Sound Card is a Realtek ALC662 6-Channel HD Audio, not what you have listed in your system specs. The first thing is to verify that you have the correct sound driver
for the RealTek from Biostar. Check the Sound in the Device Manager to see it is showing RealTek or if it's showing something else such as the generic Windows installed HD Audio Codec. The proper sound driver is the first step in proper sound device operation.
Second, go to the Control Panel/Hardware and Sound and finally the Sound Panel. Click on the Recording Tab and see if the System Mixer is shown, and if it is, it needs to be enabled and selected as the "default recording device". If it is NOT shown, RIGHT click in an empty area in that panel and then check to enable the two entries there for Show Disabled and Show Disconnected Devices. If the System Mixer now shows up, enable and then select it as the default recording device. This should fix the problem, assuming the sound module you have is capable of having both inputs at the same time.