App_AppDelegate.m no longer being called

I've been using xcode 4.0.2 for my project. I went to a computer lab today (also xcode 4.0.2) and opened up my project after downloading it from dropbox (possible corruption?) to discover that it wouldn't work when I ran the simulator. After a multitude of problems, I tried to open it on my own computer, and it also didn't work. I put NSLog(@"Hello") in the appdelegate appl开发者_运维技巧icationDidFinishLaunching -- it didn't appear. I haven't touched my project for a week, and it was working fine before -- now it suddenly does not.

I've looked on the internet at a variety of solutions (changing the compiler, changing the deployment target, deleting framework search directory) -- and none of them have worked. Any help would be great, otherwise I may have to completely copy paste my code into a new project or something like that.

The simulator shows a black screen in the computer lab. It shows a white screen on my computer.

One thing comes to mind - check if your MainWindow.xib file still has outlet connections to AppDelegate object as a delegate of File's owner (UIApplication).