Maddening Audio Problem

I used to be able to change my recording settings on the computer, my old computer.

Now I have a Windows 7 computer and everything seems quite a bit different. One, I can plug a line into the computer, in the microphone jack, and record something, like a record. At that point the built in microphone is turned off, not picking up every throat clear, etc.

But say I want to record the soundtrack of something playing on the computer, with no line in. Such as something off of You Tube. At that point, the built in microphone is still on. There doesn't seem to be any way of turning it off.

That's a bad feature ... or non-feature.