It is possible that the required audio devices are disabled in Windows. To find out, please open the Windows Control Panel. If necessary, switch the Classic View. Now open the Sounds and Audio Devices application.
In the Sounds and Audio Devices window, click the Advanced button under Device Volume.
Open the Options menu, and choose Properties.
In the Properties window that opens, select Recording. (You may have to change Mixer Device first.) Make sure that the Wave Out Mix line in the list of volume controls is checked. Click OK. The Recording Control window opens.
In this window, make sure that the Wave out Mix volume is higher than zero, and check the Select checkbox under it.
Close the Recording Control window, click OK on the Sounds and Audio Devices Properties window, and close the Control panel.
You should now be able to select Wave Out Mix in My Screen Recorder as your audio device.
If Wave Out Mix doesn't appear in the list of devices, you may need to upgrade your audio drivers.