It doesn't say what soundcard I ha ve. I'll just ask my dad lol.

before that, try to look for the stereo mix thing again, but this time, right click inside the white area and make sure to check the options marked
show disabled devices and
show disconnected devices

that's what I had to do back when i was getting bf2 working

There's only 3 devices listed under the "recording tab".
1.) Microphone
2.) Microphone (again)
3.) Line In

All of them are listed as being "High Definition Audio Devices", and listed as not plugged in.

And the show disconnected and disabled devices options are enabled.