Quicktime won't Record Line-in Audio

Hello,

I recently purchased a mid 2012 Macbook Pro 15 inch and I have the program quicktime installed.

With quicktime I am able to record my screen and record my own voice. These features work perfectly fine. However, when I try to Record "Line in" (Audio inside my computer, not my voice.) It wont record anything.

Hope you can help!

Thank you :),
Erik