Very confused as to why Audacity is no longer letting my record from a stereo mix, as in, recording what my speakers are playing. It worked perfectly last time I used it, about a week ago, and I go to do it again today, and it will no longer let me… I haven’t changed anything at all and I’m very confused. Anyone know what could possibly be wrong? Thanks in advance 
Looking into my crystal ball, I’m guessing that you used Skype last week and it changed your sound card settings.
Whatever the reason, you will need to check the settings.
First, look in the recording (Input) settings in the Device Toolbar and check that it is set to Stereo Mix. If it is set to Stereo Mix, then it should work.
If Stereo Mix is not available, then you will need to go into the Windows Sound Control Panel and check if Stereo Mix is enabled. If it isn’t, enable it and restart Audacity.
Thank you for your reply Steve. Unfortunately… that did not work 
I don’t use Skype and my stereo mix is enabled on my control panel. I also have stereo mix selected as my recording input. I don’t know what’s goin’ on cause I haven’t changed a thing since I used it last!
“Something” has obviously changed, otherwise it would still work. We need to find out “what” has changed.
Tell us about your set-up. What sort of speakers, how are they connected to your computer? What sort of sound card? What exactly are you trying to record? Which version of Windows? The more details you can give the better.
You’re right! Ha ha, nothing’s changed to my knowledge, I should say. Well, I am using an HP laptop, and just the basic speakers on the laptop itself, no external ones. I’m not sure what a sound card is… the one that came with it? Please let me know how I can let you know which one I am using ha ha. I am using Windows 7. Thanks for your time.
Help > Audio Device Info… right-click in the window > Select All, right-click again > Copy, then when you reply, press the “Code” button above where you are typing, then paste.
Have you tried these steps from scratch Audacity Manual ? Some other program may have changed your settings.
If it does not help, reboot.
If reboot does not help, perhaps a Windows update is the cause and you could see if you need to go back to earlier drivers for your built-in sound device Missing features - Audacity Support .
Gale
This is so frustrating! I rolled back my driver, restarted my computer, and then stereo mix wasn’t even an option on my Audacity input, and wasn’t an option on my device manager! So then, I updated the driver for “RealTek High Definition Audio” and restarted, and still nothing!
The problem has been fixed! Went to recording devices, “show disabled devices”, enabled Stereo Mix, and it is now working. Thanks all !