Headphones and speakers playing at the same time?

Hello....

When I plug in my headphones, my speakers just keep on playing(although the headphones also play the audio). The headphones won't show up under audio devices, and I've tried two different sets of headphones.

Does anyone know how to stop this? It was working fine yesterday....

I use Windows 7.

THANK YOU!

Do you show any hardware drivers being loaded in Windows Update?

Since you don't mention if this is a desktop or laptop, are the speakers and headphones plugged into front and back ports? What audio mixer do you normally use? There are settings for some that allow for separate audio from different outputs.