I have been having this weird problem with Xcode 4.3.2, of course after the recent update.
After successfully building and running on the simulator several times, xc
Besides a restart, there is one other way I've managed to get around this:
Let's say your app hangs, go to the targets selector in the top of the Xcode window and change your sim target to a new SDK (or if you don't have another SDK, change it to a universal app and run on the opposite device simulator).
Then, when your app loads on the new device/OS completely, quit the sim, change your targets back, et voilà!
I had the same damn issue on XCode 4.5.1, but I resolved it just now. When the program is running, it gets compiled but doesn't show anything on the simulator. just click on iOS Simulator icon in dock in order to bring it to front. Click iOS Simulator on top left -> Reset content and settings -> then force quit the iOS Simulator and run the program again. !!
I have found by chance, it is not a solution by any means -
When xcode hangs, saying it is running the app, but nothing is on simulator, opening the simulator from the dock by clicking on the dock icon (not using command+tab) seems to work.
It is very weird,but it works; atelast till xcode fixes it.
Uninstall application from Simulator and again run. Then it will works fine :)
Xcode 4.6.3 update (June 13, 2013) resolves the following issue:
https://developer.apple.com/library/mac/#releasenotes/DeveloperTools/RN-Xcode/
You can try to update your Xcode to see if that works for you..
This has frustrated me for -years- now but stumbled across what appears to get things going again for me:
Hide the simulator (iOS Simulator -> Hide iOS Simulator) or Cmd-H, then reopen the simulator.
The problem seems to happen when something CPU intensive is happening in the background (like a Time Machine backup) on my old 2 core MacBook.