Audacity controls grayed out?

whenever i use audacity and try to change the recording to stereomixer so i can record whats coming out of my speakers, the window is grayed out and i cant click on it. ive found that this problem occurs when a microphons is plugged in for some reason, and while on my desktop i merely unplug my microphone to get it to work my laptop has a built in microphone so i cant resolve the problem that ways. any suggestions on how to resolve this problem would be greatly appreciated