1. Right-click the volume control icon in the taskbar tray area, and then click Recording Devices
2. Right-click on a blank area and check Show disabled devices
3. Right-click Stereo Mix and click Enable
4. Select Stereo Mix and set it as default
5. Use software such as Windows Voice Recorder to record.
If you want to use the microphone in the future, just set the microphone as default.