The Stereo Mix on my computer isn't recording sound?

Just recently, the stereo mix on my computer won't record sound. It's been working perfectly in the past, but one day I went to record music (for a youtube video) and none of the green bars next to the stereo mix icon is showing that music is playing. If you someone could help me with this problem it would be greatly appreciated!

Go to the Device Manager, RIGHT click to higlight the RealTek audio device and then LEFT click "Uninstall". DO NOT check the box to also uninstall the drivers. Restart the PC and when Windows starts it will detect and reinstall the sound. This fixes a lot of problems and a first step to fix your problem.

Shortcut to Device Manager, Hold the Windows key down and then press the Pause/Break key. In the panel that comes up, Device Manager is in the task list in the upper left.

Thank you so much!! It's fixed

Great,glad I could help. And, thanks for the feedback that it worked.