It just happened to me. If you are in a situation where your Android Studio installation doesn't recognize any Android SDK (instead of a little andy, it shows a folder with a question mark over any Android SDK configured), you just have one diagnosis: your (hidden) configuration file is corrupted.
The solution is pretty easy. You just have to add these two lines to your /Application/Android Studio.app/bin/idea.properties:
You will be asked to reconfigure, as if it were the first execution of Android Studio.
This saved my life. You're welcome.