Not being able to hear line-in audio through the sound card's mixer, and a computer that refuses to play .WAV files; those should theoretically be two completely different and unrelated issues.

Hm. Unless, as you say, it's a configuration issue with Total Recorder. I could imagine that might do it.

Anyway, line out -> microphone in shouldn't work at all anyway. You need line out -> line in. If the computer doesn't *have* a line in, then you might be out of luck.

Also look here.