WELL, I DON'T loving KNOW THAT. YOU SHOULD AT LEAST TELL US SOMETHING.
Then you act as if it's so obvious and that I'm a fool for even mentioning the feature.
Open your volume control, find your recording devices, make sure that either Stereo Mix or Wave In are ticked (it doesn't matter if you only have one or the other). If you have neither, your sound card does not support recording from the speakers.
It happens to me. I use a headset with separate jacks for the phones and mic, so I'll try that.