1) If the sound is not recorded even though "(Default Output Device)" is selected in Bandicam, try selecting the speaker (or headphone) device directly. 2) If you still can't record computer sound, please check the Windows sound settings as shown below: If you see "Not plugged in", please connect the audio cable to your computer.
Open the Windows Device Manager and remove all incorrectly installed USB devices (device entries with a yellow exclamation mark). This is optional. Reconnect the device(s) to the system. When Windows asks for a driver, choose the inf-file(s) created above. Windows will warn that the driver is is not 'digitally signed'.