Can't Hear Line In?

I have my audio source I have plugged into line in.If i right click on the speaker icon on the tooltray, and select 'recording devices' I get the recording window - there I see the "Line In" - the bar graph next to it pumps up and down suggesting my sound reaches the PC.I then double click on "Line In", click on the "Listen" tab, and click on "Listen to this device" - but I don't hear anything.Clicking on the speaker icon i select playback devices, and right click on speakers (I tried the same thing with headphones), and click 'test' I hear the test sound. I select properties and check the levels, they are turned up.I check the Volume Mixer - the things which can be turned up are turned up.