I’m trying to use the stereo mix in the drop down menu, but my drop down menu is blank and I can’t select anything. How should I go about fixing this?
Read the appropriate Frequently Asked Question and then this Wiki page if you are on Windows, including the steps below the green panel for enabling inputs in the Windows system mixer.
If you still need help after that, post a new question to the appropriate forum for the version of Audacity and operating system you are using (for example, Audacity 1.3.x, Windows). Tell us which version of Windows you are using (for example, Vista) so we have some information to go on. This is not a “Forum issue”.