How can I record sound from the computer (not microphone) with standard tools ?
In the sound settings I see only microphone active.
You're probably trying to find the "What You Hear" (or, depending on the sound board of your PC, "What U Hear" or "Stero Mix" source), which is not visible in your posted screen shot, as opposed to the example below.
There may be a few of reasons why it is not visible:
If you're lucky, it is just hidden because it is not active. Rightclick on an empty spot of the "Sound" window, and enable both options "Show disabled devices" and "Show Disconnected Devices". If the "Stero MiX" (or equivalent) device already appears, right click on it, enable it and select it as default device.
The soundboard driver is not correctly installed or does not support the "what you hear" device. Look for the latest driver for your soundboard, and install it. Even if there's no new updates, try reinstalling the sound driver (preferably, uninstall the current version altogether, before installing the same or updated version). BTW, from your snapshot it looks like you're using the default windows driver, not a specific manufacturer's driver, and that may be the root of the problem. It that's the case look for a specific manufacturer's driver for your soundboard and install it. Then follow step 1.
Your soundboard simply does not support the "what you hear" device. Look for info on the net for your specific board ("boardxxx what you hear") to try to confirm if that's the case or not. If it is, I'm afraid you won't be able to directly record the internal sound of the PC. You may try to physically connect the output to the input of the soundboard and record from the input, but I'm not sure it will work.