Help! Only one app showing at a time!

Spaces and expose no longer work. And only one app can be shown on the desktop at any given time. If I click an app's icon it switches to that app but any other app on the desktop disappears! It doesn't close but any window not associated with the app that has been clicked in the dock instantly vanishes! This started happening randomly today and now I can't get it to fix

Anybody know of a way to fix this problem? It's giving me a headache!

Edit: Already found out what I did wrong, I had accidentally checked off "Enable Single Application Mode" under the 'Secrets' preference pane. Be careful messing around in there haha.