I’m on a macbook pro, running os 10.9.2. When I download files or record live to audacity i occasionally have no playback sound. Sometimes this is resolved by closing the program, reopening and reloading the file. Currently I am unable to resolve this. I’m using the most current version of Audacity 2.0.5.
If you connected a USB microphone, make sure you are selecting the correct playback device in Device Toolbar .
If you connected then disconnected headphones, try putting the headphones in and out several times to ensure the headphones switch is released.
Try turning off system sounds, then reboot the computer and don’t use other applications that produce sound such as QuickTime or iTunes until you have finished with Audacity.
If you installed Mavericks over a previous version of OS X, you could try reinstalling Mavericks, especially if other audio applications are giving problems.